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Chapter 3: Functional Groups/Alkanes and Cycloalkanes
Other functional groups
Thiols R-SH (skunk and additive to natural gas) Nitro R-NO2 Others like imine, enamine, sulfonate, phosphonate.
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Identify Functional Groups: Taxol (anticancer).
NH
O
O
OO
O OO
O
O
OHO
O
CH3
OH
OH
CH3
CH3
CH3
CH3
CH3
Mifepristone (RU 486) Strychnine
CH3
O
OH
NCH3
CH3
CH3
NO
O
N
Tetradotoxin—puffer fish poison Erythrosine - Red #3
O
O
OH
OH
OHOH
NH
NH2+
NH
OH
OH
I
I
O O OH
I
IOH
O
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Alkanes: Pretty inert hydrocarbons Straight Chain Saturated Hydrocarbons Name Molecular
Formula Structural Formula
Number of Isomers
Boiling Point (oC)
Methane CH4 CH4 1 -161.0 Ethane C2H6 CH3CH3 1 -88.5 Propane C3H8 CH3CH2CH3 1 -42.0 Butane C4H10 CH3CH2CH2CH3 2 0.5 Pentane C5H12 CH3(CH2)3CH3 3 36.0 Hexane C6H14 CH3(CH2)4CH3 5 68.7 Heptane C7H16 CH3(CH2)5CH3 9 98.5 Octane C8H18 CH3(CH2)6CH3 18 125.6 Nonane C9H20 CH3(CH2)7CH3 35 150.7 Decane C10H22 CH3(CH2)8CH3 75 174.1 Note these trends.
• The names are weird up to 4 and normal greek prefixes after. • The formulas and structures of these alkanes increase uniformly by CH2 • These formulas all fit the formula CnH2n+2 the highest possible H/C ratio • Since the H/C ratio in these compounds is at a maximum, we call them saturated.
Isomers result from different arrangements of molecular framework that are composed from the same molecular formula. For example, saturated arrangement of 4 carbons give two possible structures.
CC
CCH
HH
H H
HH
H
H
H C
CC C
H
HH
H
HHH
H
HH
Draw these as line structure drawings. 5 carbons:
CH3
CH2CH2
CH2CH3
CH3
CCH3 CH3
CH3CH3
CH2CH
CH3
CH3 Draw these as line structure drawings. Practice: Draw all five of the 6-carbon isomers. It helps if you name them.
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Alkyl Groups-Substituents Name Formula Condensed Formula IUPAC Name Comments Methyl -CH3 CH3 * Methyl Methyl Ethyl -CH2CH3 CH2 *CH3 Ethyl 10
Propyl -CH2CH2CH3 CH2
*CH2CH3
Propyl 10
Isopropyl -CHCH(CH3)2 CH
*CH3
CH3
(1-methylethyl)- 20 Branched
Butyl -CH2CH2CH3 CH2
*CH2CH2
CH3
Butyl 10
Isobutyl -CH2CHCH(CH3)2
CH2
*CHCH3
CH3
(2-methylpropyl) 10 Branched
sec-butyl -CH(CH3)CH2CH3 CH
*CH2CH3
CH3
(1-methylpropyl) 20
tert-butyl -C(CH3)3 C *CH3
CH3
CH3
(1,1-Dimethylethyl) 30
Systematic Naming The IUPAC rules. Steps: • Find the longest chain.
• Groups attached to the parent chain are called substituents and are named based on the number of carbons in the longest chain of that substituent, and are numbered using the number of the carbon atom on the parent chain to which they are attached.
• If the same substituent occurs more than once in a molecule, the number of each carbon of the parent chain where the substituent occurs is given and a multiplier is used to indicate the total number of identical substituents; i.e., dimethyl... trimethyl... tetraethyl..., etc.
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• Numbering of the carbons in the parent chain is always done in the direction that gives the lowest number to the substituent which is encountered first, or, the lowest number at the first point of difference. If there are different substituents at equivalent positions on the chain, the substituent of lower alphabetical order is given the lowest number.
• In constructing the name, substituents are arranged in alphabetical order, without regard for multipliers.
• When these descriptors are used in an IUPAC name, iso is alphabetized normally; the hyphenated prefixes, however (sec- and tert-) are disregarded when alphabetizing.
• A more systematic method for the nomenclature of side-chains involves identifying the longest
chain in the substituent, numbering the substituent from the point of attachment to the parent, and indicating side-chains on the substituent using the standard method described for simple alkanes. The name is enclosed in parenthesis to indicate that the numbering corresponds to the local side-chain, not the parent chain. Thus:
• an isopropyl side-chain can also be named (1-methylethyl), • a sec-butyl side-chain can also be named (1-methylpropyl), • an isopentyl side-chain can also be named (3-methylbutyl), etc.
• The origin of the prefixes sec- and tert-, given above, rests with an attempt to describe the nature of the branched carbon unit. By definition, a primary carbon is one which is attached to one other carbon atom, a secondary carbon is one which is attached to two, a tertiary carbon is attached to three, and a quaternary carbon is attached to four other carbon atoms; these are often abbreviated as 1 , 2 , 3 and 4 carbons.
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Figures and much description above from http://chipo.chem.uic.edu/web1/ocol/SB/2-1.htm Try these wacky examples. Practice: Name these C6H14 isomeric alkanes.
Petroleum Distillation A complete story of petroleum distillation can be read at the “How Stuff works” web site: http://science.howstuffworks.com/oil-refining4.htm Another good source written for chemical engineers can be found at. http://www1.cems.umn.edu/orgs/aiche/archive/history/h_refine.html
Which Fraction to Make? Various fractions are more important at different times of year. During the summer driving months, the public consumes vast amounts of gasoline, whereas during the winter more fuel oil is consumed. These demands also vary depending upon whether you live in the frigid north, or the humid south. Modern refineries are able to alter the ratios of the different fractions to meet demand, and maximize profit.
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http://www1.cems.umn.edu/orgs/aiche/archive/history/h_refine.html
Fractions Obtained from Crude Oils
Fraction Composition of carbon chains
Boiling range (oC)
Percent of crude oil
Natural Gas C1 to C4 Below 20 10% Petroleum ether (solvent) C5 to C6 30 to 60 10%
Naphtha (solvent) C7 to C8 60 to 90 10% Gasoline C6 to C12 75 to 200 40% Kerosene C12 to C15 200 to 300 10%
Fuel oils, mineral oil C15 to C18 300 to 400 30% Lubricating oil, petroleum jelly, greases, paraffin wax, asphalt
C16 to C24 Over 400 10%
http://www.3rd1000.com/chptr10.htm The outcome of burning hydrocarbons. Hydrocarbons are burned for heat and gas expansion (ICE). Burning anything in the presence of oxygen is called . The general reaction looks like this: Complete combustion CxHy + O2 à x CO2 + y/2 H2O + heat Assuming the hydrocarbon is octane, 15 gallons (avg tank of gas) burned completely in air makes about 350 lbs of CO2. 15 gal (3.8L/gal) (0.7kg/L) (1000g/kg) (1mole/114g) (8molesCO2/1moleC8H18) (44g/mole)(1kg/1000g)(2.2#/kg) = 270 lbs. Incomplete combustion: CxHy + O2 à x CO + y/2 H2O + heat
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How do we deal with the CO? What is the reaction of burning coal? What is the octane number? Some of the saturated hydrocarbons between C6 and C12 burn well and some don’t. In general, the straight chain hydrocarbons burn poorly with lots of soot. Increasing the branching of the hydrocarbons, increases the reactivity and makes the burning more efficient. On the octane scale:
CH2
CH2CH2CH3 CH2
CH2CH2
CH3
= 0
CH2
CHCCH3 CH3
CH3
CH3
CH3
= 100
The ICE needs high octane fuel to avoid afterburning or knocking. The diesel engine does best with poorer octane fuel because heat not a spark is what ignites the fuel. See http://auto.howstuffworks.com/diesel1.htm
Cycloalkanes
Name Substituent Formula Condensed formula
Line formula Angles Strain
Cyclopropane Cyclopropyl C3H6
Cyclobutane Cyclobutyl C4H8
Cyclopentane Cyclopentyl C5H10
Cyclohexane Cyclohexyl
C6H12
Cycloheptane Cycloheptyl
C7H14
Cycloalkane Cycloalkyl CnH2n
(CH2)n
Substituted cycloalkanes have 4 naming conventions that differ from alkanes.
1. If substituted, if the substituent is large or complicated then the cycloalkane can be named as a substituent.
2. The numbering starts at a substituted ring atom. 3. The numbering of more than one substituent will depend on picking the lowest possible
number combination for the substituents, with the lowest alphabetical substituent taking the lowest #. The direction may be clockwise or counterclockwise.
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Examples of the IUPAC Rules in Practice http://www.cem.msu.edu/~reusch/VirtualText/nomen1.htm#start
The following two cases provide examples of monosubstituted cycloalkanes.
More highly substituted cycloalkanes are named in a similar fashion, but care must be taken in numbering the ring.
(4) Cis-trans Since there can be no rotation around the sigma bonds in the ring, it is possible to have a new kind of isomer. This isomer has the same connectivity but different orientation in 3-D space. We indicate cis trans either with wedges and dashes or with a perspective-line projection technique. Consider 1,2-Dimethylcyclohexane
CH3
CH3H
CH3 CH3
H H
CH3 H
CH3CH3
CH3
CH3
CH3
cis -- same side
trans- opposite sidescis -- same side trans- opposite sides
H
CH3H
CH3
Unsaturation or HDI (Hydrogen Deficiency Index)
CnH2n. Loss of hydrogen content is called unsaturation. Any time a ring is made, the structure loses 2 H’s.
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Formulas for saturated hydrocarbons are CnH2n+2. The first unsaturation would give a formula CnH2n.
Consider this example:
Propane CH3CH2CH3 Cyclopropane
CH2
CH2CH2
You can see the relationship between the two structures like this.
CH2
CH2CH2CH2
CH2
CH2
**
Draw all of the isomers of C5H10 (no alkenes). Draw all of the cis-trans isomers of Dimethylcyclopropane Dimethylcyclobutane Dimethylcyclopentane
