Organic Chemistry: Introductory Topics

 Carbon forms a huge number of compounds.
 The study of the structures, reactions and
properties of these carbon-based compounds
is called organic chemistry.
 Note:
◦ Carbon monoxide, carbon dioxide, metal
carbonates and metal cyanides are not classified
as organic compounds.

2

www.wewwchemistry.com

Tetravalent
• Carbon forms four bonds.
Strong C−C bonds • Due to strong C−C bond, it
• C−C bonds are much stronger can bond with itself to form
than bonds between atoms of stable straight or branched
other elements. chains, or ring structures.

Bond Bond energy
/ kJ mol−1
Bonding Nature
C−C 350
of Carbon
Si−Si 222
Multiple bonds
N−N 160
O−O 150 • Carbon can also form
single, double or triple
bonds with itself.
• Carbon compounds can
3 have varying degree of
unsaturation.

Organic Compounds

Aliphatic Aromatic
• Saturated • Contains one
• Unsaturated or more
benzene rings
Open-chain Alicyclic Cl
• Straight-chain (closed ring)
O

OH
• Branched chain

4


Organic compounds in the same Example: alkene
homologous series:
• possess the same general formula CnH2n
• differ from the previous member in the CH2=CH2, CH2=CHCH2−H,
series by a −CH2− group CH2=CHCH2CH3, CH2=CHCH2CH2CH3
• possess similar chemical properties, • Alkenes possess a carbon-carbon
due to the presence of same functional double bond.
group • Alkenes undergo electrophilic
addition reactions.
• show gradual change in physical Etheneb.p. = −102 °C
properties due to increased molecular Propeneb.p. = −48 °C
size and mass, caused by longer 1-Butene b.p. = −6.5 °C
carbon chains 1-Pentene b.p. = 30 °C

5


 A functional group is an atom or a group of
atoms that governs the chemical properties
of an organic molecule.

6


Class of compound Functional group Name of functional group
RCH2OH Primary alcohol
RR1CHOH Secondary alcohol
Hydroxy compounds
RR1R2COH Tertiary alcohol
C6H5OH Phenol
RCHO Aldehyde
Carbonyl compounds
RR1CO Ketone

where R, R1, R2 represent alkyl groups, −CnH2n+1

8


Class of compound Functional group Name of functional group
Carboxylic acids RCO2H Carboxylic acid
RCOCl Acyl chloride
Carboxylic acid
RCO2R1 Ester
derivatives
RCONH2 Amide
RNH2 Primary amine
Amines RR1NH Secondary amine
RR1R2N Tertiary amine
Nitriles RC N Nitrile

9 where R, R1, R2 represent alkyl groups, −CnH2n+1

 The structural formulae of organic
compounds may be represented using
◦ displayed formulae
◦ condensed structural formulae
◦ skeletal formulae
 Note that any structural formula given must
give an unambiguous structure.
◦ E.g. 1-propanol
CH3CH2CH2OH ✓
C3H7OH ✗
10


 Displayed Formulae
◦ Show both the relative placing of atoms and the
number of bonds between them.
◦ All bonds between atoms must be shown.
◦ Exception:
The following convention for representing the
aromatic ring is preferred:

11


 Condensed Structural Formulae
◦ Each carbon atom is written separately.
◦ Following each of these carbon atoms,
 the other atoms that are bonded to this carbon atom
are written.
 Substituent groups that are bonded to this carbon
atom are enclosed in brackets.
◦ Similarly, the following convention for
representing the aromatic ring is preferred:

12


 Skeletal Formulae
◦ Simplified representation derived from a
structural formula by removing hydrogen atoms
(and their associated bonds) and carbon atoms
from alkyl chains, leaving just the carbon-carbon
bonds in the carbon skeleton and the associated
functional groups.
◦ The following convention for representing the
aromatic ring is preferred:

13


 IUPAC Nomenclature is a system of naming
chemical substances developed by the
International Union of Pure and Applied
Chemistry (IUPAC).
 The IUPAC sets global standards for names,
symbols, and units used in chemical sciences.

16


 The IUPAC name for an organic compound
consists of the following parts:
No. of carbon atoms in
Nature of
longest continuous carbon
parent chain
chain, i.e. parent chain

Prefix(es) Infix Root Suffix(es)

1° suffix + 2° suffix
Side chains & functional
groups of lower priority
Degree of
saturation or
unsaturation Functional group of
17
highest priority in
www.wewwchemistry.com molecule

Locants indicate
positions of
sustituent groups,
bonds etc. in
molecule

3-ethyl-4-methylhexane locant 3-oxohexanal

side-chains & infix root 1° suffix 2° suffix
functional groups of lower (nature of (no. of carbon atoms (degree of (main functional group,
priority, arranged in parent chain) in parent chain) saturation) of highest priority)
alphabetical order

locant 3-methylcyclopentene locant 2-hydroxypropanoic acid

2
1
3
18


(Source: http://en.wikipedia.org/wiki/IUPAC_nomenclature_of_organic_chemistry)

Locants indicate positions of root 1° suffix
sustituent groups, bonds etc. in (no. of carbon atoms (degree of
molecule in parent chain) saturation)

18-bromo-12-butyl-11-chloro-4,8-diethyl-5-hydroxy-15-methoxytricos-6,13-diene-19-yne-3,9-dione

tricos 23 carbons

side-chains & 2° suffix
functional groups of lower priority, (main functional group,
19
arranged in alphabetical order of highest priority)

 Punctuation rules:
◦ Di-, tri- etc. are not taken into consideration
when arranging side-chains and functional
groups alphabetically.
◦ Commas are placed between numbers.
◦ Hyphens are placed between a number and a
letter.
◦ All parts are connected either by merging
successive names, including commas or hypens
to form a one-word name.

20


 Functional groups control the chemistry of
organic molecules.
 They contain reactive sites:
◦ Electron deficient sites
 E.g. a carbon atom bonded to a more
electronegative bromine atom
◦ Electron rich sites
 E.g. a π-system in an alkene or a benzene ring

21


Types of
Bond Fission

Heterolytic Homolytic
• When a covalent bond between • When a covalent bond between two
two atoms breaks, one of the atoms breaks, each atom retains one
atoms retains both the bonding bonding electron.
electrons to bear a negative • Free radicals are formed.
charge. • A free radical is an electrically neutral
• The other atom bears a positive atom or group of atoms that has one
charge. unpaired electron. It is unstable and
highly reactive.
H−Cl→ H+ + Cl:−
Cl−Cl→Cl + Cl
23


Types of
Reagents

Electrophile Nucleophile
• A reagent that is attracted to • A reagent that is attracted to
regions of negative charge regions of positive charge or
or high electron density electron deficient sites
• An electron pair acceptor • An electron pair donor
• Good bases are generally
Positive ions: NO2+
good nucleophiles
δ+ end of an induced dipole: δ+Br−Brδ−
δ+ end of a permanent dipole: δ+H−Clδ− Negative ions: H−O:−,N C:−
Neutral molecules: H2O:, :NH3
24


 Isomers are molecules that have the same
molecular formula but different arrangement
of atoms in space.
Isomerism
Stereoisomerism
Structural isomerism
• Same molecular formula
• Same molecular formula • Same structural formula
• Different structural formulae • Different spatial arrangement
of atoms in 3D space

Cis-trans
Chain Functional Positional isomerism
isomerism isomerism isomerism
25 Optical
isomerism

 Chain Isomerism
◦ Arises due to the different arrangement of carbon
atoms in a carbon chain.
◦ E.g. isomers of hexane, C6H14

26


 Positional Isomerism
◦ Arises due to the different positions assumed by
a functional group on a carbon chain or ring.
OH
OH
OH
pentan-1-ol pentan-2-ol pentan-3-ol

CH3 CH3 CH3

Cl

Cl
2-chloromethylbenzene 3-chloromethylbenzene
Cl
4-chloromethylbenzene
27


 Cis-trans (a.k.a. geometric) isomerism
[Use of E-Z nomenclature is not required by the
9647 syllabus.]
◦ Criteria:
 Restricted rotation about a double bond, e.g.
carbon-carbon double bond, or
 Restricted rotation due to a rigid ring structure
 Two different substituent groups attached to each
atom in a double bond, e.g. to each carbon atom in
a carbon-carbon double bond

29


 Optical isomerism
◦ Criteria:
 A chiral carbon, i.e. an asymmetrical carbon atom
with four different substituent groups
 No plane of symmetry
◦ Optical isomers exist as a pair of non–
superimposable mirror images of each other.
◦ Optical isomers are also known as enantiomers.

32


 Enantiomers
◦ Identical chemical properties and physical
properties
◦ Rotate plane of polarised light in opposite
directions

33


 Racemic mixture
◦ Equal amounts of both enantiomers.
◦ Optically inactive, as there is no net rotation of
plane-polarised light. Although both enantiomers
rotate plane-polarised light in opposite
directions, the rotations cancel out.

34


 Drawing optical isomers
◦ Optical isomers must be drawn as three-
dimensional structures according to the
convention used in the example below:

35
(Source: Higher 2 Chemistry Syllabus 2013/9647)

Organic Chemistry: Introductory Topics

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Organic Chemistry: Introductory Topics

Similar to Organic Chemistry: Introductory Topics (20)

More from wewwchemistry

More from wewwchemistry (12)

Recently uploaded

Recently uploaded (20)

Organic Chemistry: Introductory Topics