CSUMB
ESSP 311 Organic Chemistry I
Ronald W. Rinehart, Ph.D.
Chapter 2 Alkanes
| Basic Organic Nomenclature by Dave Woodcock at Okanagan
University College [requires MDL Chime; use Netscape] http://www.molecularmodels.ca/nomenclature/nom1.htm |
| Organic Chemistry OnLine by Paul R.Young at the University of
Illinois at Chicago Alkanes and Cycloalkanes: Structure, Bonding, and Nomenclature tutorials [requires MDL Chime; use Netscape] http://www.chem.uic.edu/web1/OCOL-II/WIN/ALKANE/ALKANE.HTM |
| Exploring Alkanes by Gary Trammell
and Srinivas Vuppuluri at the University of Illinois at Springfield http://people.uis.edu/gtram1/organic/alkanesmenu.htm |
| Carey PowerPoint slides for chapter 2 [2.1 to 2.7,
hydrocarbon classes, functional groups, alkanes from C1 to C5, higher n-alkanes] from Columbia University can be
seen at http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/02_01_07.html |
| Carey PowerPoint slides for chapter 2 [2.8 to 2.12, IUPAC
nomenclature for alkanes and cycloalkanes] from Columbia University can be
seen at http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/02_08_12.html |
| Carey PowerPoint slides for chapter 2 [2.13 to 2.16,
sources, physical properties, chemical properties, redox in organic chem] from Columbia University can be
seen at http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/02_13_16.html |
| A set of PowerPoint slides on alkanes and
cycloalkanes
in PDF format by Paul R. Young of the University of Illinois at Chicago can be seen at http://www.chem.uic.edu/web1/PDF/CH2.PDF |
| Even though it was written for a course at a lower level,
there's lots of good stuff on hydrocarbons, alkanes, cycloalkanes, and
functional groups on my CHEM 30B "Alkanes" page http://www.mpcfaculty.net/ron_rinehart/30B/alkanes.htm |
Chapter 2. Alkanes.
To see a large number of
alkane and cycloalkane Chime structures
and particularly relevant to this section is his "Molecular Fragments:
Alkane Isomers" page at |
I. Introduction.
A. Classes of Organic Compounds
1. ~7,000,000 organic compounds.
2. Organic compounds can be characterized by
Functional Groups: the structural unit
responsible for a given molecule's chemical
behavior.
3. Functional Groups: See Tables 2.1,
2.2 or
click here
B. Types of Carbon Atoms in Organic Species:
► 1o (primary) carbons. C
bonded to 1 C (typically, a -CH3 group).
► 2o (secondary) carbons. C bonded
to 2 C's (e.g., a CH2- group).
► 3o (tertiary)
carbons. C
bonded to 3 C's (typically, a CH group).
► 4o (quaternary) carbons. C bonded
to 4 C's.
The molecule shown below has six 1o
C, three 2o C, two 3o C, and one 4o
C.
There are four
different types of
1o
C (methyl groups, CH3-), three different types of 2o
C (methylene groups, -CH2-), and two different types of 3o
C (methinyl groups, >CH-) in this molecule. These distinctions will be important
when we discuss the free-radical halogenation of alkanes [Chapter 4], and also
when we consider 1H-NMR and 13C-NMR spectra [Chapter 13].
II. Classes of Hydrocarbons.
A. Hydrocarbons.
1. Compounds composed of carbon and hydrogen.
2. Can be aliphatic or aromatic
(determined by their structure and bonding.)
B. Aliphatic Hydrocarbons.
1. Aliphatic hydrocarbons are broken into the
following categories:
a) Alkanes.
sp3
hybrids. -C-
b) Cycloalkanes
sp3
hybrids. -C-
c) Alkenes.
sp2
hybrids. C=C
d) Alkynes.
sp hybrids. C≡C
C. Aromatic Hydrocarbons.
1. Most common example: benzene. 
III. Alkanes.
A. Bonding.
1. sp3 hybridization.
2. Sigma bonds only.
3. 109.5o C< bond angles.
4. C-H bond length in CH4 = 109 pm.
5. C-C bond length in C2H6
= 153 pm.
C-H bond length in C2H6
= 111 pm.
6. Acyclic alkanes have the formula CnH2n+2
B. Nomenclature of Alkanes. IUPAC Rules.
|
IUPAC Nomenclature from ACD Labs Official IUPAC Nomenclature Home Page by G.P.
Moss at Queen Mary University of London
Nomenclature Shortcuts by Yorke E. Rhoades at Harvard University IUPAC nomenclature of hydrocarbons by Linda M. Sweeting at Towson University http://www.towson.edu/~sweeting/enrich/iupachc.pdf IUPAC nomenclature of simple organic compounds by
Linda M. Sweeting at Towson University http://www.towson.edu/~sweeting/enrich/iupac.pdf |
1. The names of the first ten [or even twenty -- see below] alkanes should be memorized:
|
methane |
CH4 |
hexane |
C6H14 or CH3(CH2)4CH3 |
|
ethane |
C2H6 or CH3CH3 |
heptane |
C7H16 or CH3(CH2)5CH3 |
|
propane |
C3H8 or CH3CH2CH3 |
octane |
C8H18 or CH3(CH2)6CH3 |
|
butane |
C4H10 or CH3CH2CH2CH3 |
nonane |
C9H20 or CH3(CH2)7CH3 |
|
pentane |
C5H12 or CH3(CH2)3CH3 |
decane |
C10H22 or CH3(CH2)8CH3 |
2. Alkyl groups are substituent groups which are attached to other atoms or parent chains.
a) They are named by dropping -ane
from the name of the corresponding alkane and
adding -yl.
b) Examples.
-CH3
methyl
-CH2CH3
ethyl
-CH2CH2CH3
propyl
3. IUPAC Rules: International Union of
Pure and Applied Chemistry.
a) Select the longest continuous
carbon chain as the "parent" structure and then
consider the attached groups.
methylpropane methylbutane
b) Where necessary indicate by
number the carbon to which the group is attached.
This number is called a
locant.
i) In numbering the
parent carbon chain start from the end closest to
the first
substituent.
3-methylpentane 2-methylpentane
c) If the same alkyl group occurs
more than once on the parent chain then indicate
this by the use of the
appropriate prefix (di-, tri-, tetra-, etc).
i) Indicate by number
the position of each group.
d) If there are several different
groups attached to the parent structure, then
list them in the name of the
compound in alphabetical order.
i) The prefixes di-,
tri-, etc are ignored when alphabetizing.
2,2,4-trimethyloctane 3,3,5-triethyl-4-methyloctane
e) Notice from the above examples that locant numbers are separated by
commas;
a number and a letter are separated by dashes.
f) When two chains are of equal
length, choose the chain with the greater number
of substituents.
4. Nomenclature of Cycloalkanes.
a) Cycloalkanes are named by adding
the prefix "cyclo" to the parent stem.
b) Notice the chemical formula of a
cycloalkane is CnH2n.
|
|
5. Name the following compounds.
a)
or
4,6-diethyl-3-methyloctane
b)
or
4-ethyl-3,5-dimethylheptane
c)
or
5,5-diethyldecane
d)
or
2,3,6,6-tetramethyloctane
e)
or 
1-ethyl-2-methyl-4-propylcyclopentane
f)
or
1,1-diethyl-3,3-dimethylcyclobutane
6. Draw structures for the following
compounds:
a) 4-ethyl-3,5-dimethylheptane
b) 4,6-diethyl-3-methyloctane
c) 1,1,3-tripropylcyclohexane
7. IUPAC rules for complex alkyl groups.
a) What difficulty arises in naming
the following compound?
i) Such alkyl groups are named with IUPAC rules or in some cases common names.
b) With IUPAC rules the substituent
group is named by taking the longest carbon
chain in the group as the parent
alkyl group and listing attached alkyl groups
with corresponding locants.
i) The above alkyl
group name is written in parentheses.
ii) In numbering the
parent chain of the alkyl group, the carbon of the
substituent group
attached to the main parent is carbon 1 of the
substituent alkyl
group.
iii) Now name the
compound in part (a).
Answer:
5-isobutylnonane or
5-(2-methylpropyl)nonane
8. Common names of some complex alkyl groups.
a) Alkyl groups with (CH3)2CH-
(on the otherwise unbranched group) whose point
of attachment to the parent is
at the opposite end is named by adding the
prefix "iso" to the name of the
alkyl group containing all carbons.
|
structure |
|
|
|
|
common name |
isopropyl |
isobutyl |
isopentyl or isoamyl |
|
IUPAC name |
(1-methylethyl) |
(2-methylpropyl) |
(3-methylbutyl) |
b) Groups with 4 carbons or more in
a straight chain but with the point of
attachment to the parent at the
second carbon gets the prefix "sec-".
|
structure |
|
|
|
|
common name |
sec-butyl |
sec-pentyl (or sec-amyl) |
sec-hexyl |
|
IUPAC name |
(1-methylpropyl) |
(1-methylbutyl) |
(1-methylpentyl) |
c) The group -C(CH3)3
is known as the tert-butyl (or t-butyl) group.
i) Name this using
IUPAC rules: (1,1-dimethylethyl)
ii) Adding an extra
carbon to this results in the t-pentyl (or t-amyl)
group:
(1,1-dimethylpropyl)
d) Some other important common
names:
|
structure |
|
|
|
common name |
neopentyl (NOT neoamyl) |
neohexyl |
|
IUPAC name |
(2,2-dimethylpropyl) |
(2,2-dimethylbutyl) |
9. Name the following compounds.
a)
b)
Answers:
a) 1,1-dimethyl-2-(1,2-dimethylpropyl)cyclopentane
b)
7-sec-butyl-5-ethyl-3,3-dimethyldecane
a better name is
5-ethyl-3,3,8-trimethyl-7-propyldecane -- at C-7, the "main" chain continues
upward. Why? Given a choice
such as this, select the main chain to include as many of the
substituents as possible.
C. Isomers.
1. As the formula of an alkane increases in
number of carbon atoms, the number of
possible constitutional isomers grows.
|
name |
# of constitutional isomers |
condensed formula of normal isomer |
|
|
1 |
methane |
1 |
CH4 |
|
2 |
ethane |
1 |
CH3CH3 |
|
3 |
propane |
1 |
CH3CH2CH3 |
|
4 |
butane |
2 |
CH3CH2CH2CH3 |
|
5 |
pentane |
3 |
CH3(CH2)3CH3 |
|
6 |
hexane |
5 |
CH3(CH2)4CH3 |
|
7 |
heptane |
9 |
|
|
8 |
octane |
18 |
|
|
9 |
nonane |
35 |
|
|
10 |
decane |
75 |
|
|
11 |
undecane |
|
|
|
12 |
dodecane |
|
|
|
13 |
tridecane |
|
|
|
14 |
tetradecane |
|
|
|
15 |
pentadecane |
4347 |
|
|
16 |
hexadecane |
|
|
|
17 |
heptadecane |
|
|
|
18 |
octadecane |
|
|
|
19 |
nonadecane |
|
|
|
20 |
eicosane |
366,319 |
|
|
22 |
docosane |
|
|
|
30 |
triacontane |
|
|
|
40 |
tetracontane |
6.249 x 1012 |
|
|
100 |
hectane |
|
CH3(CH2)98CH3 |
|
n |
gen. alkane |
|
CH3(CH2)n-2CH3 |
2. Draw all possible constitutional isomers
for alkanes of the formula:
i) C5H12
ii) C6H14
iii) C4H8
D. Physical Properties.
1. Intermolecular vs intramolecular forces of
attraction.
2. Recall 3 major forces of attraction:
a) Hydrogen bonding
b) Dipole-dipole
c) London (dispersion) forces:
induced dipole-induced dipole
3. Intermolecular force of attraction between
alkanes: London forces.
a) These weak forces result in low
boiling points for alkanes.
&nb
