TOPIC 1: ORGANIC COMPOUNDS:
ALKANES AND CYCLOALKANES
According to Chemical Abstracts, there are more than
18 million known organic compounds, each of which has its
own physical properties, such as melting point and boiling point,
as well as its own reactivity.
Chemists have learned that organic compounds can be classified into
families according to their structural features and that members of a
given family often have similar chemical behavior.
Instead of 18 million compounds with random reactivity, there are a
few dozen families of organic compounds whose chemistry is
reasonably predictable.
Throughout this course, we will study the chemistry of specific families.
I. FUNCTIONAL GROUPS
 FUNCTIONAL GROUP:
- Group of atoms within a molecule that has a characteristic
chemical behavior
- Behaves nearly the same way in every molecule
Prozac
Caffeine
Acetominophen
Vanillin
Taxol, isolated from the bark of the Pacific Yew tree, Taxus
brevifolia, is an anticancer drug, which was first studied in the
successful treatment of ovarian cancer.
In 1969, 1,200 kg of tree bark was processed to produce
10.0 g of pure taxol. The molecule contains 14 functional groups.
Taxol
Since it would be impractical to
harvest enough trees to obtain
significant amounts of taxol, a
semi-synthetic method
was developed.
Needles are harvested from a
related, low growing evergreen,
Taxus baccata, which is grown in
plantations similar to growing tea.
The needles are processed to
produce large amounts of a
synthetic precursor
10- deacetylbaccatin whose
structure is shown below.
10- deacetylbaccatin
- Synthetic precursor to taxol
- More readily available
II. ALKANES AND ALKANE ISOMERS
* You saw in Background Unit One that carbon-carbon single
bonds result from head-on overlap of carbon sp3 hybridized orbitals.
One of the unique properties of carbon is its ability to bond to
multiple carbon atoms results in long chains of atoms and the
formation of complex molecules.
 ALKANES:
- contain single carbon to carbon bonds
- hydrocarbons: contain only C & H atoms
- saturated: contain the max. number of H atoms per C atom
- have the general formula: CnH2n+2 (n = any integer)
- nonpolar
 STRAIGHT-CHAIN or NORMAL ALKANES:
- carbons atoms are connected in a row
- Ex.
 BRANCHED-CHAIN ALKANES:
- carbons atoms branch from the main chain
- Ex.
 CONSTITUTIONAL ISOMERS:
- contain the same number & types of atoms but differ in the
way the atoms are arranged
- have different chemical and physical properties
Isomer Possibilities:
Different carbon
skeletons: C4H10
Different functional
groups: C2H16O
OH
alcohol
O
ether
Different position of
functional groups:
C3H9N
NH2
NH2
* Also remember that carbon- carbon single bonds can rotate.
What may at first seem like two different molecules may
really just be the same molecule represented in two different
ways.
5
4
2
2
rotate around C-4
1
3
5
1
4
3
These two molecules are the
same; they are not isomers
III. NAMING ALKANES
* In earlier times when relatively few pure organic molecules
were known, new compounds were named at the whim of their
discoverer. Thus, urea (CH4N2O) is a crystalline substance isolated
from urine; morphine (C17H19NO3) is a painkiller named after
Morpheus, the Greek god of dreams; and barbituric acid is a tranquilizing agent named by its discoverer in honor of his friend
Barbara.
As the number of known organic compounds slowly grew, so did the
need for a systematic way of naming them. Although many
“common” naming for organic compounds still exist, the system of
naming we used is devised by the International Union of Pure and
Applied Chemistry (IUPAC, usually spoken as “eye-you-pac).
A chemical name in the IUPAC system has three parts:
prefix
Where are the
substituents?
parent
How many
carbons?
suffix
What is the
main functional
group present?
Naming Alkanes
The names of alkanes are derived from a set of prefixes, used to
indicate the number of carbons present
YOU MUST KNOW THESE!
Prefix
Formula
Prefix
Formula
meth-
C1
hex-
C6
eth-
C2
hept-
C7
prop-
C3
oct-
C8
but-
C4
non-
C9
pent-
C5
dec-
C10
The names of alkanes end in -ANE
Practice: Name the following alkanes
IV. PROPERTIES AND REACTIONS OF ALKANES
* Alkanes are sometimes referred to as “paraffins”- a word
derived from the Latin parum affinis, meaning “slight
affinity.” This term aptly describes their behavior because
alkanes show little affinity for other some substances and are,
for the most part, chemically unreactive.
PROPERTY 1: ALKANES SHOW REGULAR INCREASES IN
BOILING & MELTING POINTS AS THEIR
MOLECULAR WEIGHT INCREASES
- Due to van der Waals forces: weak intermolecular forces that
operate over small distances & occur because the electron
distribution in the molecules are non-uniform at any given
instant & create temporary dipoles
Bigger molecules
= stronger temporary dipoles
= more energy (higher temps.) needed to break the van der
Waals forces
PROPERTY 2: INCREASED BRANCHING LOWERS AN
ALKANES BOILING POINT
- Branched-chain alkanes are more spherical, have smaller
surface areas, and therefore have weaker van der Waals
forces
- Weaker van der Waals forces = lower boiling point
REACTION 1: COMBUSTION
- When hydrocarbons burn in the presence of O2, the products
are H2O and CO2
- A lot of heat is produced
- Ex. CH4
+
O2 
CO2
+
H2O
REACTION 2: RADICAL HALOGENATION
- Mixture of alkane and X2 is irradiated w/ ultraviolet light
(denoted as hυ) forming the X• radical (odd electron species)
- Products contain a variety of halogen substituted products
- Cons of reaction: difficult to control the exact spot of
halogenation (see example below) & mixtures of products form
Cl
h
Cl2
Cl
Cl Cl
Cl
Cl
etc...
V. CYCLOALKANES
 CYCLOALKANES:
- also called cyclic compounds
- consist of rings of – CH2 – units
- have the general formula: CnH2n
The general class of compounds known as steroids contain four rings
joined together- three of them six-membered rings and one of them a
five membered ring.
Cortisol, also known as hydrocortisone,
an over the counter medicine used to
treat skin irritations.
Cholesterol is essential for all animal life.
Each cell synthesizes it from simpler
molecules, a complex 37-step process.
VI. CIS-TRANS ISOMERISM IN CYCLOALKANES
* In many ways, cycloalkanes behave similar to their openchain counterparts. One difference is that cycloalkanes are
less flexible. In smaller rings (C3 – C6), rotation about the
C – C bond is impossible. This leads to the ring having a
“top” and a “bottom” side.
H
H3C
H
H
H
CH3
CH3
H3C
cannot be converted to
H
H
H
H
 STEREOISOMERS:
- atoms are connected in the same order but differ in their
spatial orientation
 CIS –TRANS ISOMERS:
- a special type of stereoisomers
- cis: means groups are on the same side
- trans: means groups are on the opposite side
CH3
H3C
H
H
H
H
cis-1,2-dimethylcyclopropane
H
H3C
H
H
CH3
H
trans-1,2-dimethylcyclopropane
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
K.
L.
1,4- dimethylcyclohexane
1-methyl-3-propylcyclopentane
3-cyclobutylpentane
1-bromo-4-ethylcyclodecane
1-chloro-3-ethyl-2-methylcyclopentane
1-bromo-3-ethyl-5-propylcyclohexane
1-fluoro-2-methylcyclobutane
1-ethyl-4-methylcycloheptane
1,1,4-trimethylcyclohexane
3-cyclopentylheptane
1,3-dimethylcyclopentane
1-ethyl-2,2,6,6-tetramethylcyclohexane
A.
3-ethyl-4-methylhexane
B.
4-ethyl-5,6-dimethyl-7-propyldecane
C.
3,4,5-triethyl-6-methyloctane
D.
3,4-diethyl-2-methylhexane
E. 1,2-diethyl-3-methylcyclohexane
F.
1,4-dibromo-2-fluorocyclopentane
G. 1-cyclopropyl-2-propylcyclopentane
H. 2-cyclopentyl-6-methyloctane
I.
5-ethyl-3-methyl-6-propylnonane