(a) Under pseudo-first-order conditions (large excess of benzaldehyde B and DBU), the authors monitored the disappearance of sulfonium tetrafluoroborate SM. What is the kinetic order of [SM] in this reaction? First order (linear plot of ln[SM] vs time)

(b) Under pseudo-first-order conditions, the following data was obtained. In each of these reactions, [B] = 0.0174 M and temperature = 298 K. What is the kinetic order of [DBU]? Entry [DBU] (M) Trendline from plot of ln[SM] vs. time (seconds/100) 1 0.0291 y = –0.0068x – 1.8296 2 0.0751 y = –0.0199x – 1.6405 3 0.113 y = –0.0329x – 1.6278 4 0.156 y = –0.0466x – 6.3816

Slope of the trendline = –kobs = k [DBU]m [B]n

entry [DBU] (M) kobs 1 0.0291 0.0068 2 0.0751 0.0199 3 0.113 0.0329 4 0.156 0.0466

SH3C

CH3

Ph O

Ph Ph

N

N

BF4

SM P

(DBU)SH3C

CH3

Phstep 1 step 2

PhCHO (B) O

PhS

Phstep 3

1 2

Problem Set 6 Answer Key

Linear relationship between kobs & [DBU], so m = 1… first-order rate dependence on [DBU]. (c) Under pseudo-first-order conditions, the following data was obtained. In each of these reactions, [DBU] = 0.156 M and temperature = 298 K. What is the kinetic order of [B]? Entry [B] (M) Trendline from plot of ln[SM] vs. time (seconds/100) 1 0.0174 y = –0.0466x – 6.3816 2 0.0433 y = –0.1103x – 1.8947 3 0.0866 y = –0.1986x – 1.7842 4 0.130 y = –0.2474x – 1.7569 5 0.173 y = –0.3022x – 1.7994 6 0.260 y = –0.3192x – 1.7368

entry [B] (M) kobs 1 0.0174 0.0466 2 0.0433 0.1103 3 0.0866 0.1986 4 0.13 0.2474 5 0.173 0.3022 6 0.26 0.3192

kobs vs. [DBU]

y = 0.3159x - 0.0029

R2 = 0.9987

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0.05

0 0.05 0.1 0.15 0.2

[DBU] (M)

ko

bs

Saturation kinetics (first-order at low [B] going to zero-order at high [B])

kobs bs. [B]

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 0.05 0.1 0.15 0.2 0.25 0.3

[B] (M)

ko

bs

mary

Rectangle

3. Please read this article: Resek & Beak. J. Am. Chem. Soc. 1994, 116,405.

(a) What is an intramolecular kinetic isotope effect experiment?

� + D OYJ fltR_ 5a.,une rviol e c.� i e�pyin-imr m�.su,rtJ U.e a.de cLfluen(e

bd-y,1eevt

we. e,IR.A Vi, C.--\..\ �J-D.

(b) Why are the values of the intramolecular and intermolecular kinetic isotope effects different?

val»e5 J jfe,- bec.tUise ',

k) �t if

'd-) �(l

a. d--s1� deprvbnairon

rLlles of- boiii ·Jeps yvuJ{if 1i t1 ml)! i I'\: twit.

i .e, I I

K _, +- k H -t- k D s;m;

4. Hayashi and co-workers developed a Wacker cyclization to convert achiral 1 into chiral benzofuran 2 in highenantioselectivity (J. Am. Chem. Soc. 2004, 126, 3036).

Pd{MeCN)4(BF 4)i {cat.) {S,S)-ip-boxax {cat.)

benzoquinone MeOH

91%, 97% ee (S.S)-ip-boxax

(a) Please draw a reasonable arrow-pushing mechanism for this transformation. @13r-4 ::: X

or

3

mary

Text Box

9.