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ORIGINAL RESEARCH
Impacts of medium, substituents, and specific interactionswith water on hydration of carbonyl compounds
Damanjit Kaur • Rajinder Kaur • Shweta Khanna
Received: 13 May 2013 / Accepted: 28 June 2013
� Springer Science+Business Media New York 2013
Abstract Theoretical study on hydration of carbonyl
compounds has been done at B3LYP/6-31??G** and MP2/
6-31??G** levels. The variations in DGhyd and hydration
constants are explored in terms of medium effect, substituent
effect, and hydrogen bonding abilities of carbonyl com-
pounds and their hydrated products. The dielectric of med-
ium decreases the DGhyd values thereby favoring the process.
The presence of electron-releasing substituents at the car-
bonyl carbon disfavors the hydration process, while that of
electron-withdrawing substituents favor the process.
Hydrogen bonding interactions stabilize the product to a
larger extent than the carbonyl molecules, thereby favoring
the hydration process. Linear correlation between the cal-
culated log Khyd values and the experimental values is seen in
case of specific interactions with water (R = 0.976) than in
the case without those interactions (R = 0.955).
Keywords Gibbs free energies � Hydration
constants � SCRF � PCM � Stabilization energies
Introduction
The hydration [1–4] of carbonyl compounds has always
generated interest because of the important role played by the
carbonyl compounds in numerous reactions involving
aqueous medium, for example, in case of bioreactions such
as those involving carbohydrates [5]. It represents one of the
simplest additions to the carbonyl group and is of the great
importance for understanding many organic reactions. Sev-
eral substituted carbonyl compounds are part of organic
synthesis and pharmaceutically [6] important compounds.
The existence of such compounds at the active sites of
enzymatic reactions [7] has been suggested to enhance the
rate of reaction. The products of hydration of aldehydes are
said to play important roles as alkylating and potentially
mutagenic agents because of reduction in their reactivity as
electrophiles [8–11]. Aldehydes and their hydrated coun-
terparts act as atmospheric pollutants [12–15].
There are several reports in the literature wherein the rate
and equilibrium constants for the addition of water to the
carbonyl compounds have been evaluated using hydration
free energies applying Marcus theory [16] and No Barrier
theory [17]. Kulkarni et al. reported the hydration patterns
and energetics of some carbonyl compounds, viz., formal-
dehyde, acetaldehyde, formamide, and acetamide, and their
studies employed restricted Hatree–Fock method and den-
sity functional theory with 6-31G(d,p) basis sets for
exploring hydration of carbonyl compounds [18]. Recently,
Hazra et al. reported gas phase hydrolysis of the simplest
carbonyl compound formaldehyde to form methanediol
catalyzed by formic acid [19]. Their studies revealed that
reaction barrier for hydrolysis significantly reduced when
single water molecule catalyzes the reaction relative to
hydrolysis with no explicit water. Moreover, they found that
reaction barrier reduced considerably with the increasing
number of water molecules, i.e., with two and three water
molecules and analyzed that the gas phase hydrolysis of
formaldehyde catalyzed by formic acid is significantly more
efficient than that involving catalysis by an equal number of
Electronic supplementary material The online version of thisarticle (doi:10.1007/s11224-013-0308-z) contains supplementarymaterial, which is available to authorized users.
D. Kaur (&) � R. Kaur � S. Khanna
Department of Chemistry, Guru Nanak Dev University,
Amritsar 143005, India
e-mail: [email protected]
R. Kaur
e-mail: [email protected]
123
Struct Chem
DOI 10.1007/s11224-013-0308-z
water molecules. Bombarelli et al. reported two approaches
to study hydration and hemiacetalization constants, named
an absolute and a relative approach to evaluate the DG
values [20]. Absolute method involves calculation of
reaction free energy directly from the differences of Gibbs
free energy of products and reactants, and log Khyd can be
evaluated using Eq. (1):
log K ¼ �DG�= ln 10RT ð1Þ
Hydration constants can be measured with a variety of
methods including UV and NMR spectroscopy [21, 22], but
owing to some limitations of these methods, computational
calculations are now a plausible alternative for deter-
mination of hydration constants.
In the present study, we investigate computational cal-
culation of hydration constants for some carbonyl com-
pounds including aldehydes, ketones, esters, and an amide
using DFT and MP2 [23, 24] theoretical methods. In par-
ticular, we have also analyzed the role of substituents and
medium through implicit and explicit interactions on the
hydration of carbonyl compounds.
Computational details
All the quantum calculations in the present study involving
ab initio molecular orbital (MO) and density functional
methods were performed using Gaussian 09W package
[25] using 6-31??G** basis sets. DFT calculations were
carried out using Becke’s three-parameter hybrid func-
tional combined with Lee–Yang–Parr correlation (B3LYP)
method, while MO calculations were done using the MP2
method. The analytic harmonic vibrational frequencies
were evaluated at the same levels to characterize the nature
of stationary points on the potential energy surface as
minimum and to account for the zero vibrational energies.
In this study, the Gibbs free energy differences for the
hydration reactions were calculated using Eq. 2 with the
following scheme in both gas phase and in medium phase:
R1 R2
O
+ H2OR1
HO OH
R2
DGhyd ¼ GR1R2C OHð Þ2 � GH2O � GR1C Oð ÞR2 ð2Þ
and the hydration constants were evaluated according to
Eq. 3:
log Khyd ¼ �DGhyd=2:303 RT ð3Þ
The DGhyd values were also evaluated for the hydration
reaction involving hydrogen-bonded reactants and products
in gas phase as well as in medium phase.
The self-consistent reaction field (SCRF) method pro-
posed by Miertus, Scrocco, and Tomasi requires that a
calculation be performed in the presence of solvent by
placing the solute in a cavity within the solvent reaction
field. The polarizable continuum model (PCM) [26–28]
using the integral equation formalism variant-PCM) is the
default SCRF method. The PCM model calculations for
Gibbs free energy in the presence of solvent, DGm [29]
includes nonelectronic contributions, namely, dispersion,
repulsion, and cavitation energies. The Gibbs free energy
change values for the hydration reactions in aqueous
medium were computed via SCRF keyword, using the
Gaussian 09W PCM input.
The adducts of carbonyl molecules under study and their
diols with single water molecule were optimized at the
above mentioned levels to analyze the effect of specific
interactions on the hydration process. The stabilization
energy for the adduct was calculated using the supermol-
ecule approach, which is defined as the difference between
the electronic energy of adduct and the combined energies
of the isolated molecules. Since the results are contami-
nated with basis set superposition error (BSSE), i.e., each
molecule in the complex may use the basis set of the other,
leading to the interaction energy overestimation; BSSE on
the stability of the aggregates has been corrected using
counterpoise (CP) method of Boys and Bernadi [30]. In this
case, CP-corrected stabilization energy DES.ECP is given by
Eq. 4:
DECPS:E ¼ EAB ABð Þ � EA ABð Þ � EB ABð Þ
� E0A Að Þ � EA Að Þ
� �� E0
B Að Þ � EB Bð Þ� �
ð4Þ
where EX(Y) is the energy of the subscript fragment X
calculated in the basis of unit Y (X = Y or X , Y); EA0 and
EB0 are the energies of the fragments A and B, respectively,
in their actual geometries within the adduct; EA(A) and
EB(B) are the respective energies of the free fragments in
their equilibrium geometries.
Results and discussion
The full optimization of the carbonyl compounds (Fig. 1)
along with their hydrated products (diols) (Fig. 2) has
been carried out at B3LYP/6-31??G(d,p) and MP2/6-
31??G(d,p) theoretical levels. The full set of geometric
parameters for the carbonyl compounds and their hydrated
products are given in Tables S1–S13 of supplementary
data. The interactions of carbonyl compounds and their
hydrated product, diols, with medium are important in
altering DGhyd values for the hydration process. The free
energy change, DGhyd(g) for the hydration reaction along
with their hydration constants were calculated in gas phase,
Struct Chem
123
H7H6
H5
H4
C3C2
O1O1
C2H3 H4
O1
C2C3 C4
H5
H6H7
H8
H9
H10
Cl5
C3
C2
O1
C4
H 7H6H8
H9
H10
F5
C3C2
O1
C4
H7H6
H8
H9
H10
HCHO CH3CHO
ClCH2CHO
CH3COCH3 FCH2COCH3ClCH2COCH3
O1
C2
C3H4
H5
H6
Cl7
O1
C2
H4
F7
C3
H5H6
FCH2CHO
O1
C2
O3
C4
H5
H6
H7
H8 H9
O1
C2
O3
C4C5
H6
H7H8
H10
H11
(CH3O)CHO (CH3O)(CH3)CO
(CH3O)(ClCH2)CO
(H2N)CHO
O1
C2
O3
C4C5
H6
H7
H8
H9
H10Cl11
O1
C2N3 H4H5
H6
O1
O3
C2
C5C4
H6
H7
H8
F11
H9
H10
(CH3O)(FCH2)CO
O1
C2
N3 C4H5
H6 H8
H7
H9
(H2N)(CH3)CO
Fig. 1 Carbonyl compounds studied
Struct Chem
123
O1
C2
O3
H6
H4
H7
H5
O3
O1
C2
H5
H9
H8
H7
C4H6H10
H9
H10H8
Cl5
H6
H7
C2
C4
O3
O1
H6
C4
C2
C5
O1
O3
H7
H8
H9
H10
H11
H12
H13
CH2(OH)2 CH3CH(OH)2
ClCH2CH(OH)2
(CH3)2C(OH)2(FCH2)(CH3)C(OH)2
Cl10
O1 H6
O3
H7
C2C4
H12
C5H9
H8
H11
H13
F10
H8
H9
H6
C2C4
H7
C5
H12
H13
H11
O1
O3
FCH2CH(OH)2
O1 H6
F5O3
H7H10C4
H9
C2
H8
(ClCH2)(CH3)C(OH)2
H10
O5
H6 C4
O3H7
C2
O1 H8
H9H11
O6
H7
C5
C3
O4
O1
C2H8
H9
H10
H11
H12 H13
H14
(CH3O)CH(OH)2 (CH3O)(CH3)C(OH)2
(CH3O)(ClCH2)C(OH)2
(H2N)CH(OH)2
O1
C2
O3
N4
H5
H6
H7
H8
H9
O1
C2
C3
O4
C5
O6
H7
H8
Cl9
H10
H11H12
H13
H14
O1H7
O4
O6
C2
C5C3
F9
H10
H8
H14
H12 H11
H13
(CH3O)(FCH2)C(OH)2
O1 H7
O3H9
N4C8
H11
H5
C2 H6H10
H12
(H2N)(CH3)C(OH)2
Fig. 2 Optimized hydrates of carbonyl compounds
Struct Chem
123
as well as in medium DGhyd(m), using the absolute approach
applying PCM model. In order to evaluate the effect of
specific interactions with water, the free energy changes of
hydration reactions and hydration constants have also been
evaluated employing adducts of carbonyl compounds and
the diols with water in gas phase and medium phase.
Gibbs free energy change and hydration constants
in gas phase
The Gibbs free energies for the hydration reaction and their
corresponding log Khyd values in gas phase are displayed in
Table 1. The hydration reactions of carbonyl compounds
under study in gas phase are endergonic. The enthalpy
changes for the hydration reactions of HCHO, CH3CHO,
ClCH2CHO, FCH2CHO, CH3COCH3, ClCH2COCH3, and
FCH2COCH3 suggest the process to be exothermic (Table
S14 in supporting information) in nature thereby suggest-
ing that it is the entropy change accompanying the process,
which makes the process unfavorable in gas phase. The
presence of –OCH3 and –NH2 substituents at the carbonyl
carbon makes the process endothermic, and hence, the
hydration of the carbonyl compounds carrying these sub-
stituents is also disfavored energetically.
With consideration of Gibbs free energy change and
hydration constants in gas phase (Table 1), results show
Table 1 DGhyd(g), DGhyd(m) (in kcal/mol), and respective log Khyd
values for hydration reactions of carbonyl compounds without explicit
water molecule and with explicit water molecules in gas phase and
medium phase (in the presence of water as solvent) at B3LYP/6-
31??G(d,p) and MP2/6-31??G(d,p) theoretical levels
Carbonyl compounds DGhyd(g) DGhyd(m) log Khyd
MP2 (B3LYP) MP2 (B3LYP) Gas phase MP2 (B3LYP) Medium phase MP2 (B3LYP)
HCHO 4.40 (3.93) -7.04 (-6.30) -3.24 (-2.90) 5.18 (4.63)
CH3CHO 7.27 (8.75) -4.14 (-5.40) -5.35 (-6.45) 3.05 (3.97)
ClCH2CHO 5.90 (7.93) -7.59 (-5.42) -4.34 (-5.83) 5.58 (3.99)
FCH2CHO 5.80 (7.30) -7.75 (-4.28) -4.27 (-5.37) 5.70 (3.15)
CH3COCH3 9.64 (13.14) -2.05 (-0.23) -7.09 (-9.68) 1.51 (0.17)
ClCH2COCH3 6.78 (8.22) -6.36 (-5.63) -4.99 (-6.05) 4.68 (4.14)
FCH2COCH3 6.18 (7.45) -6.48 (-5.74) -4.55 (-5.48) 4.77 (4.22)
(CH3O)CHO 17.61 (18.46) 6.89 (3.58) -12.96 (-13.58) -5.08 (-2.64)
(CH3O)(CH3)CO 18.94 (22.03) 8.56 (10.09) -13.94 (-16.21) -6.30 (-7.43)
(CH3O)(ClCH2)CO 17.28 (20.71) 7.60 (13.36) -12.72 (-15.24) -5.59 (-9.83)
(CH3O)(FCH2)CO 16.64 (19.97) 6.16 (12.58) -12.25 (-14.69) -4.53 (-9.26)
(H2N)CHO 17.61 (19.93) 8.91 (13.22) -12.96 (-14.67) -6.56 (-9.73)
(H2N)(CH3)CO 18.15 (23.18) 9.25 (16.14) -13.36 (-17.06) -6.81 (-11.88)
HCHO–H2O 1.16 (0.43) -12.10 (-12.86) -0.86 (-0.32) 8.91 (9.46)
CH3CHO–H2O 6.55 (8.48) -6.80 (-7.08) -4.82 (-6.24) 5.00 (5.21)
ClCH2CHO–H2O 4.05 (6.61) -10.52 (-6.38) -2.98 (-4.86) 7.74 (4.70)
FCH2CHO–H2O 4.94 (6.61) -9.93 (-6.25) -3.63 (-4.86) 7.31 (4.60)
CH3COCH3–H2O 6.05 (10.88) -5.93 (-1.91) -4.45 (-8.00) 4.37 (1.41)
ClCH2COCH3–H2O 3.34 (8.51) -7.89 (-1.90) -2.45 (-6.26) 5.81 (1.40)
FCH2COCH3–H2O 2.88 (7.71) -8.00 (-2.01) -2.12 (-5.67) 5.88 (1.48)
(CH3O)CHO–H2O 16.01 (18.31) 4.48 (7.12) -11.78 (-13.48) -3.30 (-5.24)
(CH3O)(CH3)CO–H2O 18.68 (23.21) 7.15 (11.93) -13.75 (-17.08) -5.27 (-8.78)
(CH3O)(ClCH2)CO–H2O 15.44 (20.12) 4.74 (11.39) -11.36 (-14.81) -3.49 (-8.39)
(CH3O)(FCH2)CO–H2O 15.52 (20.77) 4.71 (10.89) -11.43 (-15.29) -3.45 (-8.01)
(H2N)CHO–H2O 17.82 (21.10) 6.47 (11.50) -13.11 (-15.53) -4.76 (-8.46)
(H2N)(CH3)CO–H2O 18.01 (23.06) 7.29 (14.49) -13.25 (-16.97) -5.37 (-10.66)
HCHO–(H2O)2 0.81 (0.61) -13.06 (-16.48) -0.60 (-0.45) 9.62 (12.13)
HCHO–(H2O)3 0.78 (0.95) -11.86 (-14.40) -0.57 (-0.70) 8.74 (10.59)
HCHO–(H2O)4 -7.22 (-6.29) -21.74 (-21.25) 5.31 (4.63) 16.01 (15.64)
CH3CHO–(H2O)2 4.05 (6.91) -9.42 (-8.01) -3.00 (-5.08) 6.93 (5.90)
CH3CHO–(H2O)3 4.18 (6.95) -8.19 (-6.14) -3.08 (-5.11) 6.03 (4.52)
CH3CHO–(H2O)4 3.53 (6.83) -8.34 (-6.35) -2.60 (-5.02) 6.14 (4.67)
Struct Chem
123
that hydration reactions are relatively more favorable for
aldehydes (HCHO, CH3CHO, ClCH2CHO, and FCH2
CHO) than for ketones (CH3COCH3, ClCH2COCH3,
FCH2COCH3, etc.). The highest and positive DGhyd(g)
value is for (CH3O)(CH3)CO (18.94 kcal/mol), and hence,
hydration is the least favored for this carbonyl compound.
Comparison of DGhyd(g) values for hydration of ClCH2
CHO (5.90 kcal/mol) and FCH2CHO (5.80 kcal/mol) rel-
ative to CH3CHO (7.27 kcal/mol) and ClCH2COCH3
(6.78 kcal/mol); and FCH2COCH3 (6.18 kcal/mol) relative
to that of CH3COCH3 (9.64 kcal/mol) suggest that elec-
tron-releasing substituents at the carbonyl carbon disfavor
the hydration process, while the electron-withdrawing
substituents favor the process. The DGhyd(g) values for
hydration of (CH3O)CHO, (CH3O)(CH3)CO, (CH3O)
(ClCH2)CO, and (CH3O)(FCH2)CO are 17.61, 18.94,
17.28, and 16.64 kcal/mol, respectively, while for CH3
CHO, CH3COCH3, ClCH2COCH3, and FCH2COCH3, the
values are 7.27, 9.64, 6.78, and 6.18 kcal/mol, respectively,
suggesting the dominating role of substituent –OCH3 in the
former series. The log Khyd values also reflect that hydra-
tion of aldehyde is easier in comparison with similarly
substituted ketone. The presence of electron-withdrawing
substituents –Cl and –F both in case of aldehydes and
ketones increases its susceptibility to undergo hydration,
while electron-donating substituents like –CH3, –NH2
(p-donor) decrease the hydration ability of carbonyl com-
pounds. As can be seen from the table, in the presence of
–OCH3 substituent, the log Khyd values suggest the con-
siderable decrease in hydration ability of the carbonyl
compound.
Effect of medium on free energy change of hydration
The Gibbs free energies for the hydration reaction and their
corresponding log Khyd values were also calculated in
medium phase and are placed in the same table (Table 1).
By including effect of dielectric of the medium, the
DGhyd(m) value for the hydration process becomes negative
for HCHO, CH3CHO, ClCH2CHO, FCH2CHO, CH3CO
CH3, ClCH2COCH3 and FCH2COCH3 but remains positive
for the rest of the carbonyl compounds under study.
However in case of latter, there is decrease in DGhyd(m) in
comparison to the DGhyd(g), thus the results suggest the
importance of implicit interactions. Figure 3 depicts the
plot of calculated log Khyd values versus the experimental
values [16, 31–34] for each of two theoretical methods for
the hydration of carbonyl compounds in medium without
consideration of specific interactions with water. It can be
seen that the DFT-B3LYP/6-31??G(d,p) values are well
correlated with R value 0.945. On the other hand, MP2/6-
31??G(d,p) values are more correlated (R = 0.955) than
DFT-B3LYP method. In sum, the MP2 results are more
accurate than B3LYP results for all the carbonyl com-
pounds under study.
Effect of substituents on the hydration process
In order to explore the effects of substituents on the relative
stability of carbonyl compounds and diols and hence the
hydration process, the DGiso for following sets of isodesmic
reactions have been evaluated. The values are recorded in
Table 2.
HCHO þ RCH3 ! RCHO þ CH4
CH3COCH3 þ RCH2CH3 ! CH3C ¼ Oð ÞR þ CH4
CH2 OHð Þ2þ RCH3 ! RCH OHð Þ2þ CH4
CH3ð Þ2C OHð Þ2þ RCH3 ! Rð Þ CH3ð ÞC OHð Þ2þ C2H6
Nearly all the substituents under study stabilize the
carbonyl moiety with exception of two in ketones. The
highest stabilization is realized with –OCH3 substituent
followed by that due to –NH2 group. The stabilization
effect of –ClCH2 and –FCH2 is much lower in comparison
to that of –CH3, and their substitution on CH3COCH3
results in destabilization as reflected by the positive DGiso
value. The –OCH3 substituent remains the most stabiliz-
ing in ketones as well. The strong stabilization effects of
(a)
(b)
log Khyd (exp)
-10
-5
0
5
10
-15 -10 -5 0 5
(R =0.945)
log
Khy
d(c
alc)
-10
-8
-6
-4
-2
0
2
4
6
-15 -10 -5 0 5
(R = 0.955)
log Khyd (exp)
log
Khy
d(c
alc)
Fig. 3 Correlation between the experimental and calculated log Khyd
values in medium at (a) B3LYP/6-31??G(d,p), (b) MP2/6-
31??G(d,p) levels
Struct Chem
123
–NH2 and –OCH3 on the stability of carbonyl compounds
have been traced to arise from the conjugative interactions
between the lone pair of electrons present at N and O of
the two substituents, respectively, with pC–O MO of the
carbonyl compound from NBO analysis (Table S15 in
supporting information). The diols are also stabilized by
the presence of substituents; however, the stabilization is
lower in magnitude in comparison to the value for
respective carbonyl molecules. The difference in
DDG values for the isodesmic reaction reflects the dif-
ference in the relative stabilities of carbonyl compound
and its respective diol, and it is observed that it is of the
same order as DDGhyd(g) for the hydration of the carbonyl
compound. Thus, the increase in DDGhyd(g) for hydration
in gas phase arises because of stronger stabilization of the
carbonyl compound in comparison to the stabilization of
the product.
Effects of explicit interactions on the hydration reaction
of carbonyls
The hydrogen-bonded adducts of the carbonyl compounds
and the diols have been optimized at both B3LYP and MP2
levels and are shown in Figs. 4 and 5, and the full set of
geometric parameters are given in Tables S16–28 in sup-
plementary data. For the carbonyl compounds with several
potential energy minimum structures, the most stable con-
former of the compound is selected for H-bonded adduct
formation. The hydrogen bond (H-bond) distances in the
adducts range between 1.890 and 2.551 A, which reflect the
effect of substituent on the H-bond strengths with the well-
known fact that, the shorter the H-bond, the stronger is the
H-bond. The H-bond angles O���H–A vary between 111.10
and 163.83�. The adducts HCHO–H2O, CH3CHO–H2O,
ClCH2CHO–H2O, FCH2CHO–H2O, (CH3O)CHO–H2O,
and (H2N)CHO–H2O are stabilized through single inter-
molecular H-bond between two monomeric units with car-
bonyl oxygen as H-bond acceptor. The optimized geometries
for the adducts CH3COCH3–H2O, ClCH2COCH3–H2O,
FCH2COCH3–H2O, (CH3O)(CH3)CO–H2O, (CH3O)(ClCH2)
CO–H2O, (CH3O)(FCH2)CO–H2O, and (H2N)(CH3)CO–H2O
reflect the presence of second H-bond involving O of H2O as
H-bond acceptor to C–H of methyl substituent.
The presence of methyl substituent at the carbonyl
functionality increases its H-bond acceptor ability as
reflected by the stabilization energy for the CH3CHO–H2O
adduct (5.19 kcal/mol at MP2 level) which is 0.41 kcal/
mol greater than that for HCHO–H2O adduct. The above
fact is also supported by the stabilization energy for the
adduct CH3COCH3–H2O (5.84 kcal/mol) which is
0.65 kcal/mol higher than that of CH3CHO–H2O. With the
presence of –Cl and –F in case of adducts ClCH2CHO–
H2O and FCH2CHO–H2O, the stabilization energies are
4.44 and 4.40 kcal/mol, which are 0.75 and 0.79 kcal/mol,
respectively, lower in comparison to that of CH3CHO–
H2O. The stabilization energies of adduct formations of
CH3COCH3, ClCH2COCH3, and FCH2COCH3 with water
are 5.84, 5.61, and 5.70 kcal/mol, respectively, indicating
the marginal effects of –Cl and –F on the H-bond ability of
these molecules. The strongest stabilization is realized with
(H2N)(CH3)CO as H-bond acceptor to water among all the
adducts under study. The adducts of HCHO with two,
three, and four water molecules (Fig. 6) are stabilized by
two, four, and six H-bonds, respectively, with stabilization
energies of 9.23, 17.22, and 25.10 kcal/mol, respectively.
On the other hand, adducts of CH3CHO with two, three,
and four water molecules are adorned with three, five, and
six H-bonds and stabilization energies of 10.15, 18.17, and
24.98 kcal/mol, respectively (Table 3).
Table 2 DGiso values for the set of isodesmic reactions of carbonyl
compounds in gas phase and medium phase at B3LYP/6-31??G(d,p)
(L1) and MP2/6-31??G(d,p) (L2) theoretical levels
Reference HCHO CH3COCH3
Substituent Gas Medium Gas Medium
L2 (L1) L2 (L1) L2 (L1) L2 (L1)
CH3 -11.46 -10.73 – –
(-11.98) (-11.98)
ClCH2 -7.63 -4.76 5.09 4.62
(-7.89) (-5.25) (5.94) (5.69)
FCH2 -6.10 -3.23 7.41 6.66
(-6.87) (-4.67) (6.68) (6.06)
OCH3 -33.65 -31.69 -22.54 -20.46
(-33.15) (-31.98) (-21.41) (-19.65)
NH2 -32.38 -32.43 -19.25 -19.76
(-33.57) (-34.47) (-20.73) (-20.75)
Reference CH2(OH)2 (CH3)2C(OH)2
Substituent Gas Medium Gas Medium
L2 (L1) L2 (L1) L2 (L1) L2 (L1)
CH3 -8.61 -7.83 – –
(-7.17) (-11.08)
ClCH2 -6.16 -5.31 -0.76 0.30
(-3.91) (-8.36) (1.02) (5.45)
FCH2 -4.73 -3.54 0.96 2.23
(-3.51) (-2.66) (0.83) (5.29)
OCH3 -20.47 -17.76 -13.24 -9.85
(-18.63) (-22.10) (-12.52) (-9.79)
NH2 -19.19 -16.48 -10.74 -8.46
(-17.58) (-14.95) (-10.70) (-4.84)
Struct Chem
123
O1 H5
O6
O1
O9
H8
O1 H8
O9
O1 H8
O9
O1
H11O12
C4
H8
O1O12
H11
C4H8
O12O1
H11
C4
H8
HCHO-H2O
ClCH2CHO-H2O
CH3CHO-H2O
FCH2CHO-H2O
CH3COCH3-H2O ClCH2COCH3-H2O FCH2COCH3-H2O
O1 H9
O10
O1H12
H9
O13
O1
H12
O13
H9
O1
O13
H12
O1
H9
O1 H7
H10
O11
H7
(CH3O)CHO-H2O (CH3O)(CH3)CO-H2O
(CH3O)(ClCH2)CO-H2O (CH3O)(FCH2)CO-H2O
(H2N)CHO-H2O (H2N)(CH3)CO-H2O
Fig. 4 Optimized adducts of carbonyl compounds with water
Struct Chem
123
In order to understand the impact of intermolecular
interactions with water on the relative stability of hydrated
carbonyl compounds; the adducts of diols with water have
also been optimized and are shown in Fig. 5. The important
distances and angles that are indicative of H-bonds are
produced in Table 4. The stabilization energies associated
O8
H10
O1 H5
O3
O1 H5 O11
O3H13
H6O1O11
H13O3
O1 H6O11
O3H13
O1 H6
O3
O1
O14
H15
H6 O14
O3 H15
O1O14
H6
O3 H15
CH2(OH)2-H2O CH3CH(OH)2-H2O
ClCH2CH(OH)2-H2O
(CH3)2C(OH)2-H2O
FCH2CH(OH)2-H2O
(ClCH2)(CH3)C(OH)2-H2O (FCH2)(CH3)C(OH)2-H2O
O1 H13
H11
O12
O1 H16
O15O6 H14O5
O1H16
H14O15
O6
O1 H7O10
N4H12
O1 H7
O13
H15N4
(CH3O)(CH3)C(OH)2-H2O(CH3O)CH(OH)2-H2O
(CH3O)(ClCH2)C(OH)2-H2O (CH3O)(FCH2)C(OH)2-H2O
(H2N)CH(OH)2-H2O (H2N)(CH3)C(OH)2-H2O
O1 H16
O6O15
H16
Fig. 5 Optimized adducts of hydrates of carbonyl compounds with water
Struct Chem
123
with aggregation are also included in the same table.
Figure 7 depicts the adducts of diols of formaldehyde and
acetaldehyde with water in 1:2, 1:3, and 1:4 ratios. The
adducts of diols with water has stabilization energies which
range from 6.98 to 37.65 kcal/mol at MP2/6-31??G(d,p)
theoretical level.
All the adducts of diols with water in 1:1 ratio (with
exception of two adducts) reflect two H-bonds, one
involving O–H of diol as H-donor and another as O of
second O–H group of diol as H-bond acceptor. The two
H-bonds in the adduct CH2(OH)2–H2O stabilize the adduct
formation with energy of 7.82 kcal/mol which is 3.04 kcal/
mol greater than the value in the case of HCHO–H2O. The
increase in stabilization energy of adduct formation as the
result of the presence of –CH3 substituent is more pro-
nounced in the case of diols in comparison to the relevant
effect in the cases of HCHO–H2O and CH3CHO–H2O.
With the presence of –Cl and –F at one of the methyl
substituents in (XCH2)(CH3)C(OH)2, the stabilization
energy increases by 0.24 and 0.31 kcal/mol at the MP2
level for the adduct with water relative to the adduct
(CH3)2C(OH)2–H2O. The adduct (CH3O)CH(OH)2–H2O
has been stabilized by energy of 7.84 kcal/mol which is
comparable to that of CH2(OH)2–H2O; similar is the result
for the adduct (CH3O)(CH3)C(OH)2–H2O with respect to
CH3CH(OH)2–H2O. The placements of –Cl and –F at the
methyl substituent in the adducts (CH3O)(ClCH2)C(OH)2
–H2O and (CH3O)(FCH2)C(OH)2–H2O, leads to the
formation of two H-bonds each with comparable stabil-
ization energy relative to the remaining –OCH3-substituted
adducts. The adduct (H2N)CH(OH)2–H2O has two,
O1–H7���O10 and N4���H12–O10, H-bonds with the stabil-
ization energy of 8.14 kcal/mol which is only 0.06 kcal/mol
greater than the value for CH3CH(OH)2–H2O (8.08 kcal/
mol). In contrast, the adduct (H2N)(CH3)C(OH)2–H2O has
the stabilization energy of 8.44 kcal/mol which is 1.15 kcal/
mol greater than (CH3)2C(OH)2–H2O. In the adducts of
CH2(OH)2 and CH3CH(OH)2 with water in 1:2, 1:3, and 1:4
ratios, the number of H-bonds are larger in the adducts of
diols in comparison with the adducts of carbonyl com-
pounds; hence, the stabilization energies resulting from the
explicit interactions are relatively larger in the former
adducts. Therefore, increasing the number of explicit inter-
actions by increasing the number of water molecules favors
the hydration process.
The enthalpy changes (Table S14 in supporting infor-
mation) evaluated for the hydration of H-bonded adducts of
carbonyl compounds with single water molecule under
study indicate that H-bonding favors the hydration process.
This is reflected by the change in DGhyd(g) value (Table 1)
for the hydration process involving H-bonded adducts as
well, which is understandable as the specific interactions of
diols with water are stronger in comparison with the inter-
actions of respective carbonyl compounds. Upon further
inclusion in H-bonding interactions with two, three, and four
water molecules in the adducts of HCHO and CH2(OH)2, the
DGhyd(g) values decrease further and become negative in
case of adducts with four water molecules. However, with
increasing explicit H-bonding interactions in case of
hydration of CH3CHO and its diol with one, two, three, and
four water molecules, the decrease in DGhyd(g) is reflected,
but the decrease is relatively less marked. The same trends
were observed in the case of medium phase: the DGhyd(m)
values decrease with increasing explicit interactions with
water as can be seen from the same table. Similar evalua-
tions could not be carried out for the rest of the molecules
because of resource constraints. Thus, although the DGhyd
values for the hydration process remain positive in cases of
carbonyl compounds having –OCH3 or –NH2 substituents,
the explicit interactions involving large number of water
molecules and the medium effect can make the process
feasible. Figure 8 depicts the plot of log Khyd values calcu-
lated versus the experimental values for hydration of car-
bonyl compounds including both the effects of specific
interactions with water and medium. The plot indicates a
linear correlation coefficient of 0.976, and its comparison
with Fig. 3 (R = 0.955) at MP2/6-31??G** suggests that
the hydration is more favorable with inclusion of specific
interactions with single water molecule. The intercepts for
the plots reflect the magnificent difference between the
calculated and experimental values. In view of good
HCHO-(H2O)2 CH3CHO-(H2O)2
HCHO-(H2O)3 CH3CHO-(H2O)3
HCHO-H2O)4 CH3CHO-(H2O)4
O1
C2H3 H4
H5
O6
H7H8
O9
H10O1
C2C3
H4H5
H6 H7
H8
O9
H10
H11O12
H13
O1
C2H3H4
H5
O6
H7
H8
O9
H10
H11
O12H13
O1
C2C3 H4
H5
H6H7
H8O9
H10
H11
O12
H13
H14
O15H16
O1
C2H3H4
H5O6
H7
H8
O9
H10
H11
O12H13
H14
O15 H16
O1
C2C3
H4
H5
H6 H7
H8O9
H10H11O12
H13
H14
O15H16
H17
O18
H19
Fig. 6 Optimized adducts of carbonyl compounds with two, three,
and four water molecules (only for formaldehyde and acetaldehyde)
Struct Chem
123
Table 3 The hydrogen bond distances, angles, atomic charges, and stabilization energies (DECorr)# in adducts of carbonyl compounds with water
at MP2/6-31??G** level
Species H-bond distances (A) H-bond angles (h) Atomic charges DECorr
HCHO–H2O O1���H5 2.013 O1–H5–O6 146.85 qO(qH) -0.642(0.516) 4.78
CH3CHO–H2O O1���H8 1.968 O1–H8–O9 152.27 qO(qH) -0.670(0.517) 5.19
ClCH2CHO–H2O O1���H8 2.040 O1–H8–O9 142.99 qO(qH) -0.649(0.515) 4.44
FCH2CHO–H2O O1���H8 2.038 O1–H8–O9 143.14 qO(qH) -0.660(0.515) 4.40
CH3COCH3–H2O O1���H11 1.935 O1–H11–O12 163.18 qO(qH) -0.692(0.522) 5.84
O12���H8 2.505 O12–H8–C4 137.01 qO(qH) -1.026(0.263)
ClCH2COCH3–H2O O1���H11 1.962 O1–H11–O12 157.99 qO(qH) -0.659(0.520) 5.61
O12���H8 2.461 O12–H8–C4 133.09 qO(qH) -1.024(0.273)
FCH2COCH3–H2O O1���H11 1.966 O1–H11–O12 157.38 qO(qH) -0.657(0.520) 5.70
O12���H8 2.474 O12–H8–C4 129.22 qO(qH) -1.025(0.274)
(CH3O)CHO–H2O O1���H9 2.008 O1–H9–O10 147.16 qO(qH) -0.739(0.517) 4.89
(CH3O)(CH3)CO–H2O O1���H12 1.941 O1–H12–O13 161.13 qO(qH) -0.751(0.522) 5.71
O13���H9 2.541 O13–H9–C5 134.50 qO(qH) -1.024(0.262)
(CH3O)(ClCH2)CO–H2O O1���H12 1.998 O1–H12–O13 149.69 qO(qH) -0.729(0.521) 5.53
O13���H9 2.324 O13–H9–C5 140.82 qO(qH) -1.022(0.287)
(CH3O)(FCH2)CO–H2O O1���H12 1.983 O1–H12–O13 149.88 qO(qH) -0.754(0.520) 5.52
O13���H9 2.551 O13–H9–C5 111.10 qO(qH) -1.025(0.236)
(H2N)CHO–H2O O1���H7 1.930 O1–H7–O8 153.80 qO(qH) -0.761(0.522) 6.18
(H2N)(CH3)CO–H2O O1���H10 1.890 O1–H10–O11 163.83 qO(qH) -0.776(0.526) 6.90
O11���H7 2.528 O11–H7–C4 126.22 qO(qH) -1.031(0.269)
HCHO–(H2O)2 O1���H5 2.039 O1–H5–O6 143.09 qO(qH) -0.681(0.515) 9.23
O1���H8 2.039 O1–H8–O9 143.08 qO(qH) -0.681(0.515)
HCHO–(H2O)3 O1���H5 2.017 O1–H5–O6 145.86 qO(qH) -0.707(0.515) 17.22
O1���H8 1.928 O1–H8–O9 162.32 qO(qH) -0.707(0.533)
O9���H11 1.883 O9–H11–O12 157.94 qO(qH) -1.033(0.532)
O12���H4 2.242 O12–H4–C2 149.25 qO(qH) -1.038(0.188)
HCHO–(H2O)4 O1���H5 1.913 O1–H5–O6 163.66 qO(qH) -0.734(0.534) 25.10
O1���H8 1.913 O1–H8–O9 163.67 qO(qH) -0.734(0.534)
O6���H14 1.884 O6–H14–O15 158.01 qO(qH) -1.034(0.531)
O9���H11 1.884 O9–H11–O12 157.98 qO(qH) -1.034(0.531)
O12���H4 2.257 O12–H4–C2 149.60 qO(qH) -1.037(0.183)
O15���H3 2.262 O15–H3–C2 149.58 qO(qH) -1.037(0.183)
CH3CHO–(H2O)2 O1���H8 1.995 O1–H8–O9 147.80 qO(qH) -0.709(0.519) 10.15
O1���H11 1.987 O1–H11–O12 157.31 qO(qH) -0.709(0.516)
O12���H5 2.477 O12–H5–C2 138.66 qO(qH) -1.020(0.265)
CH3CHO–(H2O)3 O1���H8 1.893 O1–H8–O9 164.07 qO(qH) -0.735(0.534) 18.17
O1���H11 1.972 O1–H11–O12 160.04 qO(qH) -0.735(0.519)
O9���H14 1.877 O9–H14–O15 158.99 qO(qH) -1.036(0.532)
O12���H5 2.513 O12–H5–C3 138.39 qO(qH) -1.020(0.261)
O15���H4 2.257 O15–H4–C2 152.27 qO(qH) -1.037(0.196)
CH3CHO–(H2O)4 O1���H8 1.903 O1–H8–O9 163.79 qO(qH) -0.751(0.534) 24.98
O1���H11 1.897 O1–H11–O12 175.45 qO(qH) -0.751(0.536)
O9���H14 1.879 O9–H14–O15 158.61 qO(qH) -1.035(0.531)
O12���H17 1.867 O12–H17–O18 162.84 qO(qH) -1.033(0.529)
O15���H4 2.254 O15–H4–C2 154.81 qO(qH) -1.036(0.195)
O18���H5 2.329 O18–H5–C3 176.87 qO(qH) -1.032(0.274)
The distances are in A, angles in degrees, and stabilization energies in kcal/mol
Struct Chem
123
Table 4 The hydrogen bond distances, angles, atomic charges, and stabilization energies (DECorr)# in adducts of hydrates of carbonyl com-
pounds with water at MP2/6-31??G**
Species H-bond distances (A) H-bonding angles (h) Atomic charges DECorr
CH2(OH)2–H2O O3���H10 2.025 O3–H10–O8 135.18 qO(qH) -0.847(0.525) 7.82
O8���H5 2.033 O8–H5–O1 140.41 qO(qH) -1.031(0.531)
CH3CH(OH)2–H2O O3���H13 1.957 O3–H13–O11 140.88 qO(qH) -0.857(0.528) 8.08
O11���H5 1.983 O11–H5–O1 145.98 qO(qH) -1.029(0.536)
ClCH2CH(OH)2–H2O O3���H13 2.033 O3–H13–O11 136.11 qO(qH) -0.846(0.525) 7.65
O11���H6 1.959 O11–H6–O1 145.11 qO(qH) -1.025(0.540)
FCH2CH(OH)2–H2O O3���H13 2.042 O3–H13–O11 135.94 qO(qH) -0.847(0.525) 7.58
O11���H6 1.972 O11–H6–O1 143.71 qO(qH) -1.025(0.538)
(CH3)2C(OH)2–H2O O3���H15 1.967 O3–H15–O14 142.48 qO(qH) -0.852(0.525) 7.29
O14���H6 2.046 O14–H6–O1 144.31 qO(qH) -1.030(0.530)
(ClCH2)(CH3)C(OH)2–H2O O3���H15 2.054 O3–H15–O14 135.81 qO(qH) -0.843(0.522) 7.05
O14���H6 2.022 O14–H6–O1 143.87 qO(qH) -1.027(0.535)
(FCH2)(CH3)C(OH)2–H2O O3���H15 2.066 O3–H15–O14 135.44 qO(qH) -0.844(0.522) 6.98
O14���H6 2.037 O14–H6–O1 142.50 qO(qH) -1.026(0.533)
(CH3O)CH(OH)2–H2O O1���H13 2.043 O1–H13–O12 135.89 qO(qH) -0.837(0.526) 7.84
O12���H11 1.980 O12–H11–O5 144.85 qO(qH) -1.029(0.539)
(CH3O)(CH3)C(OH)2–H2O O1���H16 2.032 O1–H16–O15 137.11 qO(qH) -0.844(0.527) 8.05
O15���H14 1.978 O15–H14–O6 147.87 qO(qH) -1.028(0.539)
(CH3O)(ClCH2)C(OH)2–H2O O1���H16 2.082 O1–H16–O15 130.10 qO(qH) -0.849(0.543) 8.42
O15���H14 1.934 O15–H14–O6 148.82 qO(qH) -1.027(0.548)
(CH3O)(FCH2)C(OH)2–H2O O1���H16 2.098 O1–H16–O15 129.85 qO(qH) -0.849(0.526) 8.15
O15���H14 1.949 O15–H14–O6 148.27 qO(qH) -1.026(0.545)
(H2N)CH(OH)2–H2O O10���H7 1.924 O10–H7–O1 153.82 qO(qH) -1.031(0.538) 8.14
N4���H12 2.017 N4–H12–O10 144.16 qO(qH) -0.973(0.529)
(H2N)(CH3)C(OH)2–H2O O13���H7 1.917 O13–H7–O1 154.52 qO(qH) -1.032(0.542) 8.44
N4���H15 1.986 N4–H15–O13 145.81 qO(qH) -0.966(0.531)
CH2(OH)2–(H2O)2 O3���H10 1.880 O3–H10–O8 149.30 qO(qH) -0.883(0.528) 13.57
O8���H7 2.063 O8–H7–O1 142.52 qO(qH) -1.035(0.526)
O11���H4 1.882 O11–H4–O3 175.78 qO(qH) -1.006(0.537)
CH2(OH)2–(H2O)3 O1���H14 1.900 O1–H14–O15 171.89 qO(qH) -0.854(0.521) 19.02
O3���H10 1.913 O3–H10–O8 144.66 qO(qH) -0.878(0.529)
O8���H7 1.978 O8–H7–O1 144.32 qO(qH) -1.034(0.541)
O11���H4 1.874 O11–H4–O3 174.69 qO(qH) -1.009(0.539)
CH2(OH)2–(H2O)4 O1���H17 1.772 O1–H17–O18 166.70 qO(qH) -0.883(0.544) 37.65
O3���H14 1.915 O3–H14–O15 162.66 qO(qH) -0.874(0.529)
O8���H7 1.786 O8–H7–O1 163.39 qO(qH) -1.050(0.553)
O11���H4 1.812 O11–H4–O3 163.86 qO(qH) -1.038(0.546)
O15���H9 1.806 O15–H9–O8 155.87 qO(qH) -1.043(0.544)
O18���H12 1.869 O18–H12–O11 151.32 qO(qH) -1.063(0.539)
O18���H16 2.224 O18–H16–O15 139.53 qO(qH) -1.063(0.518)
CH3CH(OH)2–(H2O)2 O3���H13 1.868 O3–H13–O11 149.19 qO(qH) -0.885(0.530) 13.67
O11���H5 2.037 O11–H5–O1 144.94 qO(qH) -1.035(0.530)
O14���H6 1.890 O14–H6–O3 176.30 qO(qH) -1.006(0.536)
CH3CH(OH)2–(H2O)3 O1���H17 1.899 O1–H17–O18 168.90 qO(qH) -0.859(0.521) 19.20
O3���H13 1.889 O3–H13–O11 145.75 qO(qH) -0.881(0.531)
O11���H5 1.957 O11–H5–O1 147.91 qO(qH) -1.034(0.543)
O14���H6 1.879 O14–H6–O3 174.60 qO(qH) -1.008(0.539)
Struct Chem
123
correlation shown in the Fig. 3, the intercept arises because
of systematic error in evaluating fully the effect of envi-
ronment on the free energy change for the hydration process.
The plots of log Khyd calculated values in the absence of
specific interactions (Figure S1) and in the presence of such
interactions (Figure S2) in gas phase are also linear;
however, the correlation coefficient is relatively lower
than that obtained in the case of medium (Figs. 3 and 8,
respectively).
Conclusions
The present study evaluates the free energy changes and
hydration constants for the hydration of selected carbonyl
compounds reaction in gas phase, in medium, and
combination of explicit interactions with water and effect
of medium. The hydration of carbonyl compounds is sug-
gested to be endergonic in gas phase. The presence of
Table 4 continued
Species H-bond distances (A) H-bonding angles (h) Atomic charges DECorr
CH3CH(OH)2–(H2O)4 O1���H17 1.813 O1–H17–O18 175.36 qO(qH) -0.868(0.539) 26.60
O3���H13 1.889 O3–H13–O11 144.87 qO(qH) -0.882(0.532)
O11���H5 1.935 O11–H5–O1 148.62 qO(qH) -1.034(0.546)
O14���H6 1.878 O14–H6–O3 175.05 qO(qH) -1.008(0.539)
O18���H20 1.854 O18–H20–O21 167.23 qO(qH) -1.040(0.529)
O21���H7 2.459 O21–H7–C4 168.50 qO(qH) -1.032(0.249)
The distances are in A, angles in degrees, and stabilization energies in kcal/mol
Dr = rvw-r, rvw (Sum of van der Waal radii) = rO ? rH = 2.60 A; rS ? rH = 3.05 A; rN ? rH = 2.7
O1
C2
O3H5
H4
H6
H7
O8
H9
H10
O11
H12
H13
O1
C2 O3
C4
H5
H6
H7
H8
H9
H10
O11
H12
H13
O14
H15H16
CH2(OH)2-(H2O)2 CH3CH(OH)2-(H2O)2
O1
C2
O3
H4
H5
H6
H7O8
H9
H10
O11
H12
H13
H14
O15
H16
CH2(OH)2-(H2O)3 CH3CH(OH)2-(H2O)3
O1
C2O3H4
H5H6
H7
O8H9
H10
O11
H12
H13
H14
O15H16
H17
O18
H19
CH2(OH)2-(H2O)4 CH3CH(OH)2-(H2O)4
O1
C2
O3C4
H5
H6
H7
H8
H9
H10
O11H12
H13
O14
H15H16
H17O18
H19
H20
O21H22
O1 H5
O3
O11
H13
H12
H6
O14
H15H16
H7
H9
H8
H10
H17
H19
O18
C2
C4
Fig. 7 Optimized adducts of hydrates of carbonyl compounds with
two, three, and four water molecules (only for formaldehyde and
acetaldehyde)
(a)
(b)
-6
-4
-2
0
2
4
6
8
10
-10 -8 -6 -4 -2 0 2 4
(R = 0.975)
log
Khy
d(c
alc)
log Khyd (exp)
-10
-5
0
5
10
-10 -8 -6 -4 -2 0 2 4
log Khyd (exp)
log
Khy
d(c
alc)
(R = 0.976)
Fig. 8 Correlation between the experimental and calculated log Khyd
values for adduct containing single water molecule in medium phase
at (a) B3LYP/6-31??G(d,p), (b) MP2/6-31??G(d,p) levels
Struct Chem
123
electron-releasing substituents at the carbonyl carbon dis-
favors the hydration process, while electron-withdrawing
substituents favor the process. The substituents –NH2 and
–OCH3 on carbonyl moiety have remarkable effect on
DGhyd(g) value in disfavoring the process. Inclusion of the
effect of dielectric of medium through PCM model shows
decrease in DGhyd values. In order to evaluate the effect of
substituent on hydration, the values of DGiso accompanying
isodesmic reactions indicate that the stabilization of car-
bonyl compounds is greater than that of the hydrated product
in the molecules under study. The conjugative interactions
between the lone pair of electrons present at substituent on
the carbonyl group in case of –NH2 and –OCH3 are
responsible for their significant effects on the hydration
ability of the substituted carbonyl compound. The inclusion
of explicit interactions between hydrogen-bonded reactants
and products reflected that these interactions favor the pro-
cess as the products are more stabilized than the reactants.
Supporting information
Tables S1–S13 include the optimized parameters for the
carbonyl compounds along with their hydrated products
(diols) at B3LYP/6-31??G** and MP2/6-31??G** the-
oretical levels. The enthalpy changes in gas phase
(DHhyd(g)) for hydration reactions of carbonyl compounds
are given in Table S14. Important second-order stabiliza-
tion energies E(2)(kcal/mol) associated with orbital inter-
actions in carbonyl compounds and their adducts with
water at MP2/6-31??G(d,p) theoretical levels are reported
in Table S15. Geometric parameters for hydrogen-bonded
adducts of carbonyl compounds and their respective diols
at the same theoretical levels are given in Tables S16–S28.
The important distances and angles for H-bonding inter-
actions for the adducts of HCHO and CH3CHO along with
their hydrated products involving two, three, and four
water molecules are included in Tables S29–S34. Figure S1
(without specific interactions with water) and Figure S2
(with specific interactions with water) include plots com-
paring calculated log Khyd values with experimental values
in gas phase for both the theoretical levels.
Acknowledgments The authors are highly thankful to DST
(INSPIRE Fellowship Programme) for the financial assistance.
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