Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

An
Introduction
to
Organic
Chemistry

81

An Introduction to Organic Chemistry

Organic Chemistry
Organic chemistry is the study of compounds
containing carbon with the exception of simple
compounds e
...
carbonates (CO32-), carbon
dioxide (CO2) and carbon monoxide (CO)
...
Nomenclature is therefore very
important
...
You will get
practice at this in your tutorials
...

This will give you the base of the name:
No of C atoms
1
2
3
4
5
6
7
8
9
10

Name
meth-ane
eth-ane
prop-ane
but-ane
pent-ane
hex-ane
hept-ane
oct-ane
non-ane
dec-ane
82

An Introduction to Organic Chemistry

2) Determine the principle functional group and
its position
...

Position need not be indicated for alkanes, as
they have no functional group, and aldehydes
and acids, as they are terminal functional
groups
...
Multiple positions for a given
functional group are separated by commas
and indicated by the prefixes di, tri, tetra,
penta, hexa, hepta, octa , nona and deca
...

ancilliary
functional group
methyl
ethyl

formula
-CH3
-C2H5

prefix
methyl
ethyl
83

An Introduction to Organic Chemistry

propyl
butyl
pentyl
hexyl
heptyl
octyl
nonyl
decyl
fluorine
chlorine
bromine
iodine
amine
hydroxyl
cyanide
benzyl
phenyl

-C3H7
-C4H9
-C5H11
-C6H13
-C7H15
-C8H17
-C9H19
-C10H21
-F
-Cl
-Br
-I
-NH2
-OH
-CN
-CH2C6H5
-C6H5

propyl
butyl
pentyl
hexyl
heptyl
octyl
nonyl
decyl
fluoro
chloro
bromo
iodo
amino
hydroxy
cyano
benzyl
phenyl

Empirical and Molecular Formulae
Quantitative elemental analysis tells us what
elements make up a compound and in what
proportions
...
C,
H, S and N burn to give CO2, H2O, SO2 and NO2
...


84

An Introduction to Organic Chemistry

How is this done? First some definitions:
One mole of a substance is 6
...
This huge value is termed
Avogadro’s number
...

Relative molecular mass is the sum of the
relative atomic masses (RAMs) of the constituent
elements in the compound
...
g
...
010 g mol-1) + (6 x 1
...
999 g mol-1)
= 46
...
152 g of an organic compound X containing
only C, H and O produces:
0
...
091 g of H2O
upon total combustion
...

Consider the CO2
CO2 RMM = 12
...
999 g mol-1 = 44
...
223 g of CO2 = 0
...
008 g mol-1 = 5
...
07 x 10-3 mol of CO2 were produced from 5
...
07 x 10-3 mol x 12
...
061 g
% C in X = 100% x 0
...
152 g = 40
...
006 g mol-1 + 15
...
011 g mol-1
0
...
091 g / 18
...
05 x 10-3 mol
5
...
01 x 10-2 mol of H
The mass of C = 1
...
006 g mol-1 = 0
...
010 g / 0
...
7%

Consider the O
% O in X = 100% - 40
...
7% = 53
...

C
relative mass %
40
...
010
relative mole %
3
...
6
1
...
6
2

O
53
...
999
3
...
The molecular formula could be
any multiple of the empirical formula e
...

C2H4O2, or C3H6O3 since these would all have
the same percentage mass ratios
...
05 x 10-3 mol of C means 5
...
152 g
RMM of X = 0
...
05 x 10-3 g mol-1 = 30
...

86

An Introduction to Organic Chemistry

Structural
Formulae

and

Isomerism

Structural

Different arrangements of atoms for a given
molecular formula are often possible
...

Example one: C4H10
CH3CH2CH2CH3
HH
H

C

HH
C

HH

C

CH3CHCH3CH3
H

C
HH

H

H

C H
H C
H
C H H
H
C
H

H

87

An Introduction to Organic Chemistry

Example two: C2H6O
CH3CH2OH

H

CH3OCH3

HH

H

HH

HH

C

O

C

C

C

H

O

H

HH

OH

O

Both exemplify structural isomerism
...

CH3HC2CH2CH3 is a structural formula as it
shows constituent atoms AND connectivities
...

This is known as stereoisomerism
...

88

An Introduction to Organic Chemistry

Geometric isomerism
It is possible for single C-C bonds to rotate
freely, however, double C=C bonds cannot
...

H

COOH

H

COOH

cis-isomer
Z(

Zusammen - together)

HOOC
H

H
COOH

trans-isomer
E ( Entgegen - opposite)

Geometric isomers have different physical and
chemical properties

89

An Introduction to Organic Chemistry

Optical isomerism
A carbon atom attached to four different groups
(substituents) is termed a chiral centre
...


These mirror images are called enantiomers
...

Rotation to right termed dextro or d
Rotation to left termed laevo or l
They have identical chemical properties except
towards optically active reagents
...
Such a mixture is termed a
racemic mixture or a racemate
...
The drug thalidomide,
prescribed to pregnant women as a powerful
sedative from 1956 exists as two enantiomers
...
The other
caused human transmutation…

91

An Introduction to Organic Chemistry

Hybridisation
The simplest organic molecule is methane CH4
...

How and why does carbon form 4 bonds?

Promotion of one of the two 2s electrons
increases energy but the formation of four bonds
causes a four-fold decrease
...

ALL tetrahedral carbon and
nitrogen atoms in organic chemistry are sp3
hybridised
...
The unused p
orbital on each carbon overlaps to form the π
part of the double bond, e
...
ethene
...
The unused p orbitals
on each carbon overlap to form the π parts of the
triple bond, e
...
ethyne (acetylene)

---