Organic Chemistry
Chapter 12
Organic Chemistry
• Organic chemistry: the study of the
compounds of carbon
– organic compounds are made up of carbon and
only a few other elements
– chief among these are hydrogen, oxygen, and
nitrogen
– also present are sulfur, phosphorus, and a
halogen (fluorine, chlorine, bromine, or iodine)
Organic Chemistry
– the experiment of Wöhler in 1828 was the first
in a series of experiments that led to the demise
of the vital force theory
NH4 Cl + AgNCO
A mmonium Silver
ch loride
cyan ate
heat
O
H2 N-C-NH2 + AgCl
U rea
Silver
chloride
Organic Chemistry
• The link to biochemistry
– carbohydrates, lipids, proteins, enzymes,
nucleic acids, hormones, vitamins, and almost
all other chemicals in living systems are organic
compounds
Organic Structure
– Make a model of each of these structures:
HH
H
C C
HH
Eth ane
(bond angles
109.5°)
H
H
Eth ylen e
(bond angles
120°)
H-C C-H
H-C-C-Cl :
Acetylene
(bond an gles
180°)
HH
Ch loroeth ane
(bond angles
109.5°)
H-C-O-H
C O
H
H
HH
Methanol Formald ehyde Methan amin e
(b ond angles (bond angles
(bond angles
109.5°)
120°)
109.5°)
H
:
H
H-C-N-H
:
: :
: :
H
: :
H-C-C-H
H
HH
H
C N
H
H
Methyleneimine
(bond angles 120°)
Organic Structure
– VSEPR model: the most common bond angles
are 109.5°, 120°, and 180°
HH
H
C C
HH
Eth ane
(bond angles
109.5°)
H
H
Eth ylen e
(bond angles
120°)
H-C C-H
H-C-C-Cl :
Acetylene
(bond an gles
180°)
HH
Ch loroeth ane
(bond angles
109.5°)
H-C-O-H
C O
H
H
HH
Methanol Formald ehyde Methan amin e
(b ond angles (bond angles
(bond angles
109.5°)
120°)
109.5°)
H
:
H
H-C-N-H
:
: :
: :
H
: :
H-C-C-H
H
HH
H
C N
H
H
Methyleneimine
(bond angles 120°)
Functional Groups
• Functional group: anything other than just C-C, or
C-H bonds!
• Functional groups are important because
– they undergo the same types of chemical reactions no
matter in which molecule they are found
– to a large measure they determine the chemical and
physical properties of a molecule
– Naming is based on FG.
Functional Groups
• Five important functional groups
Family
Functional
group
Example
N ame
Alcoh ol
-OH
CH3 CH2 OH
Eth anol
Amine
-NH2
CH3 CH2 NH2
Eth anamin e
Ald ehyde
O
-C-H
O
CH3 CH
Eth anal
Ketone
O
-C-
O
CH3 CCH3
Aceton e
Carb oxylic acid
O
-C-OH
O
CH3 COH
Acetic acid
Chapter 11
Alkanes and
Cycloalkanes
Alkanes
• Alkanes: hydrocarbons containing only
carbon-carbon single bonds
– the first two alkanes are methane and ethane
H
H-C-H
H
Methane
HH
H-C-C-H
HH
Eth ane
Alkanes
• line-angle formula:
– a line represents a carbon-carbon bond and an angle
represents a carbon atom
– a line ending in space represents a -CH3 group
– hydrogen atoms are not shown in line-angle formulas
Ball-andstick model
Line-an gle
formula
Conden sed
structu ral
formula
CH3 CH2 CH3
Propan e
CH3 CH2 CH2 CH3
Butane
CH3 CH2 CH2 CH2 CH3
Pen tane
Alkanes
– the first 10 alkanes with unbranched chains
Name
Conden sed
Molecu lar Stru ctural
Formula Formula
Name
Conden sed
Molecu lar Stru ctural
Formula Formula
CH4
CH3 CH3
hexane C6 H1 4
CH3 ( CH2 ) 4 CH3
heptane C7 H1 6
CH3 ( CH2 ) 5 CH3
CH3 CH2 CH3
octan e
C8 H1 8
CH3 ( CH2 ) 6 CH3
C4 H1 0
CH3 ( CH2 ) 2 CH3
non ane C9 H2 0
CH3 ( CH2 ) 7 CH3
pentane C5 H1 2
CH3 ( CH2 ) 3 CH3
decane
methan e CH4
eth ane
C2 H6
propan e C3 H8
butane
C1 0 H2 2
CH3 ( CH2 ) 8 CH3
Constitutional Isomerism
• Constitutional isomers: compounds that
have the same molecular formula but
different structural formulas
– for the molecular formulas CH4, C2H6, and
C3H8, only one structural formula is possible.
– for the molecular formula C4H10, two
constitutional isomers are possible
CH3 CH2 CH2 CH3
Bu tane
(bp -0.5°C)
CH3
CH3 CHCH3
2-Methylp ropan e
(bp -11.6°C)
Constitutional Isomerism
– Problem: do the structural formulas in each set
represent the same compound or constitutional
isomers?
(each is C6H 1 4)
(a) CH3 CH2 CH2 CH2 CH2 CH3 and CH3 CH2 CH2
CH2 CH2 CH3
CH3
CH3
(b) CH3 CHCH2 CH and CH3 CH2 CHCHCH3
CH3
CH3
CH3
(each is C7 H 16 )
Constitutional Isomerism
– Solution:
(a) they represent the same compound
2
2
6
4
3
1
1
3
5
4
1
2
3
4
5
1
6
CH3 CH2 CH2 CH2 CH2 CH3
and
2
3
CH3 CH2 CH2
4
1
2
3
5
4
CH3
CH3 CHCH2 CH
CH3
CH3
and CH3 CH2 CHCHCH3
5
1
2
3
4
5
5
4
6
CH2 CH2 CH3
– Solution:
(b) they represent constitutional isomers
CH3
6
5
4
3
2
CH3
1
5
3
2
1
Constitutional Isomerism
– Problem: draw structural formulas for the five
constitutional isomers of molecular formula
C6H14
Constitutional Isomerism
– Problem: draw structural formulas for the five
constitutional isomers of molecular formula
C6H14
– Solution:
2
1
4
3
6
5
Six carb ons in an
un branched chain
4
1
2
3
2
5
1
4
3
2
5
Five carb ons in a ch ain;
one carbon as a b ran ch
1
4
3
2
1
4
3
Four carbons in a chain;
two carbons as branch es
IUPAC Names
• The IUPAC name of an alkane with an
unbranched chain of carbon atoms consists of two
parts:
– (1) a prefix: the number of carbon atoms in the chain
– (2) the suffix -ane: shows that the compound is a
saturated hydrocarbon
Prefix
methethpropbu tpen t-
N umber of
Carb on Atoms
1
2
3
4
5
Prefix
hexheptoctnon dec-
N umber of
Carb on Atoms
6
7
8
9
10
IUPAC Names
• The name of an alkane with a branched
chain of carbon atom consists of
– a parent name: the longest chain of carbon
atoms
– substituent names: the groups bonded to the
parent chain
su bstituen t
paren t chain
CH3
1
2
3
4
5
6
7
6
8
CH3 CH2 CH2 CHCH2 CH2 CH2 CH3
1
4-Methyloctane
2
4
3
8
5
7
IUPAC Names
• Alkyl group: a substituent group
– named by dropping the -ane from the name of
the parent alkane and adding the suffix -yl
N ame
methyl
Con dens ed
Structu ral Formula
-CH3
ethyl
-CH2 CH3
propyl
-CH2 CH2 CH 3
isopropyl -CHCH3
CH 3
bu tyl
-CH2 CH2 CH 2 CH3
N ame
isobu tyl
sec-butyl
Con dens ed
Structu ral Formula
-CH2 CHCH3
CH3
-CHCH2 CH3
CH3
CH 3
t ert-bu tyl -CCH3
CH 3
IUPAC Names-Review
1. The name for an alkane with an unbranched chain
of carbon atoms consists of a prefix showing the
number of carbon atoms and the ending -ane
2. For branched-chain alkanes, longest chain of
carbon atoms is the parent chain
3. Name and number each substituent on the parent
chain; use a hyphen to connect the number to the
name
CH3
CH3 CHCH3
1
2
3
2-Methylprop ane
IUPAC Names-Details
4. If there is one substituent, number the
parent chain from the end that gives the
substituent the lower number
CH3
CH3 CH2 CH2 CHCH3
4
5
3
2
2-Methylpen tane
(n ot 4-methylpentan e)
1
IUPAC Names-Details
5. If the same substituent occurs more than
once,
– indicate the number of times the substituent
occurs by a prefix di-, tri-, tetra-, penta-, hexa-,
and so on
– use a comma to separate position numbers
CH3 CH3
CH3 CH2 CHCH2 CHCH3
6
4
5
2
3
2,4-Dimethylhexan e
(n ot 3,5-d imethylhexan e)
1
IUPAC Names- Details
6. If there are two or more different substituents
– list them in alphabetical order
– number the chain from the end that gives the lower
number to the substituent encountered first
– if numbering is the same in both directions, give the
substituent of lower alphabetical order the lower
number
CH3
CH3 CH2 CHCH2 CHCH2 CH3
2
1
4
3
CH2 CH3
3-Ethyl-5-methylhep tane
(not 3-methyl-5-ethylheptan e)
6
5
7
IUPAC Names-Details
7. Do not include the prefixes di-, tri-, tetra-, and so
on, or the hyphenated prefixes sec- and tert- in
alphabetizing;
– alphabetize the names of substituents first, and then
insert these prefixes
CH3 CH2 CH3
6
4
2
1
5
CH3 CCH2 CHCH2 CH3
3
CH3
4-Eth yl-2,2-d imethylhexan e
(n ot 2,2-d imethyl-4-ethylhexane)
Common Names
• Common names- older system
CH3
CH3 CHCH3
CH3
CH3 CH 2 CHCH3
Isobu tane
Isopentane
– use the IUPAC system for our class!
Cycloalkanes
Alkanes whose carbon atoms are joined in rings are called
cycloalkanes. They have the general formula CnH2n where n =
3,4,…
24.2
Cycloalkanes
• Cyclic hydrocarbon: a hydrocarbon that contains
carbon atoms joined to form a ring
• Cycloalkane: a cyclic hydrocarbon in which all
carbons of the ring are saturated
– cycloalkanes of ring sizes ranging from 3 to over 30
carbon atoms are found in nature
– five-membered (cyclopentane) and six-membered
(cyclohexane) rings are especially abundant in nature
Cyclopentan e
Cycloh exane
Cycloalkanes
• Nomenclature
– Prefix cyclo-,
– if only one substituent, no location number
– if there are two substituents, number the ring
beginning with the substituent of lower
alphabetical order.
Name These Cycloalkanes
Conformations - Alkanes
– Molecules move a lot … each movement result in a
different conformation … each conformation has an
associated energy … some conformations are more
stable than others!
– following are three conformations for a butane
molecule
rotate
by 120°
Least crow ded
conformation
rotate
by 60°
Intermed iate
crow din g
Most crow d ed
conformation
Cyclopropane
Hydrogen's move
to alleviate
eclipsing energies
Cyclobutane
Cyclopentane
Cyclopentane
• The most stable conformation of a
cyclopentane ring is an envelope
conformation
Cyclohexane
H
H
H
H
H
H
Axial hydrogens shown
Cyclohexane
• The most stable conformation of a
cyclohexane ring is the chair conformation
– all bond angles are approximately 109.5°
Cyclohexane
• In a chair conformation,
– six C-H bonds are equatorial
– six C-H bonds are axial
axis th rough the
cen ter of th e rin g
H
H
H
H H
H
H
H
(a) Ball-and-s tick mod el
sh ow ing all 12 hydrogen s
H
(b) The s ix eq uatorial
C-H bond s
H
H
H
(c) The s ix axial
C-H b on ds
Draw the Chair
Cyclohexane
– the more stable conformation of a substituted
cyclohexane ring has substituent group(s)
equatorial rather than axial
CH3
CH3
Equatorial methylcyclohexane
Axial methylcyclohexane
Axial vs. Equatorial
Which is more stable?
Cl
vs.
Cl
Cycloalkanes cis and trans
H3C
CH3
CH3
cis-1,2-dimethylcyclopropane
CH3
cis-1,2-dimthylcyclobutane
H3C
CH3
CH3
CH3
trans-1,2-dimethylcyclopropane
trans-1,2-dimthylcyclobutane
If a ring has two
substituents on
it, they can be on
the same side
(cis) or the
opposite side
(trans).
Cis-Trans Isomers
– alternatively, we can view it from above
H3 C
CH3
cis-1,2-D imethylcyclopentan e
H3 C
CH3
t rans-1,2-D imeth ylcyclopentan e
Cis-Trans Isomers
– to determine cis-trans isomers if cis-trans isomers
are possible, we can view a cyclohexane ring as a
planar hexagon
CH3
H
CH3
H
CH3
H
or
H3 C
H
CH3
trans -1,4-D imethylcyclohexane
or
H3 C
CH3
CH3
cis-1,4-D imethylcyclohexane
– because cis-trans isomers differ in the orientation
of their atoms in space, they are stereoisomers
– cis-trans isomers are one type of stereoisomers
Alkane Nomenclature-Review
1. Find the longest continuous chain of carbon atoms in
the molecule. This is the “parent” name. … or the ring
is the parent.
2. Branched are named as an alkyl group.
3. Substituents are numbered in the direction that gives
the smaller numbers for the locations of the branches.
4. Use prefixes di-, tri-, tetra-, when there is more than
one alkyl branch of the same kind.
5. Use previous rules for other types of substituents.
Write them in alphabetical order.
24.2
What is the IUPAC name of the following compound?
CH3
CH3
1
CH
2
C2H5
CH2
3
CH
4
CH2
5
CH2
6
CH2
7
CH3
8
4-ethyl-2-methyloctane
What is the structure of 2-ethyl-4-methylhexane? Can
you name it properly?
C2H5
CH3
CH3
1
CH
2
CH2
3
CH
4
CH2
5
CH3
6
True Name: 3,5-dimethlyheptane
24.2
Alkane Chemistry
Key reactions:
1) Burning
• CH4 + O2  CO2 + H20 + Heat
2) Chlorination
• CH3CH3 + Cl2  CH3CH2Cl + HCl
•
Note that multiple chlorination reactions
can occur in uncontrolled environments.
Monochlorinate Butane
1) When butane is chlorinated, the C1 and C2
products are different.
2 structural isomers
*
Cl
Cl
1-chlorobutane
2-chlorobutane
•A chiral carbon
•See CH 15
Formation of 2-chlorobutane
Mechanism of formation
Cl
Cl
+ Cl
2 Cl
.
+ HCl
H
H
Planer
Intermediate
.
+ Cl
H
Cl
Both mirror images
0ptically different