General Chemistry

Lecture-5-

College of Pharmacy

Organic Chemistry

1

2019-2020

Organic Chemistry

Alkanes

• Alkanes: are saturated hydrocarbons (paraffin) that is

contain only carbon and hydrogen bonded together through

carbon-hydrogen and carbon-carbon single bonds. They are

either straight- chain or branched-chain hydrocarbons, with

general formula CnH2n+2

Contain C-C single bonds & (no functional group)

Tetrahedral geometry

sp3 hybridized carbons

o All hydrocarbons are nonpolar molecules. As a result they

are not water soluble but are soluble in nonpolar organic

solvents.

o they have relatively low melting points and boiling points

and are generally less dense than water.

o The longer the hydrocarbon chain (greater the molecular

weight), the higher the melting and boiling points and the

greater the density (see next slide).

Molecules having the same molecular formula but different

arrangements of atoms are called structural or constitutional

isomers.

Physical Properties of Alkanes

o Alkyl group are alkanes with one fewer hydrogen atom.

Nomenclature of Alkanes

Carbon atoms are classified according to the number of

other carbon atoms to which they are attached.

Primary carbon (1ᵒ) is directly bonded to one other carbon.

Secondary carbon(2ᵒ) is bonded to two other carbon atoms.

Tertiary carbon (3ᵒ) is bonded to three other carbon atoms

Quaternary carbon (4ᵒ) is bounded to four carbon atoms.

Steps in Nomenclature of Alkanes

1. Identify the parent chain:

Choose the longest chain.

Parent Names for Alkanes

Parent + ane = Name of alkane

If there is a competition between two chains of equal length,

then choose the chain with the greater number of substituents.

o Substituents are the groups connected to the parent chain:

Ex/Identify and provide a name for the parent in the

following compound:

Example: Identify and name the parent in each of the

following compounds:

Answers:

a) parent= hexane

2. Identify and Name the Substituents.

Substituents are named with the same terminology used

for naming parents; only we add the letters (yl).

Alkane – 1H = Alkyl substituent

e.g.

Methane – H= methyl

CH4-H = -CH3

Alkane alkyl group

Ethane Ethyl group

Once the parent has been identified, the next step is to

list all of the substituents:

• Example: Identify and name all substituents

in the following compound:

3. Number the parent chain and assign a locant to each

substituent:

o If one substituent is present, it should be assigned the lower

possible number.

o When multiple substituents are present, assign numbers so that

the first substituent receives the lower number.

o If there is a tri, then the second locant should be as low as possible:

o When a substituent appears more than once in a compound, a prefix

is used to identify how many times that substituent appears in the

compound (di = 2, tri = 3, tetra = 4, penta = 5, and hexa = 6).

For example, the compound above would be called

• 2,3,6-trimethylheptane.

Notice that a hyphen (-) is used to separate numbers from letters,

while commas are used to separate two numbers from each other.

4. Arrange the substituents alphabetically:

Once all substituents have been identified and assigned

the proper locants, they are placed in alphabetical order.

Ex/ Provide a systematic name for the following compound:

Many common names persist in organic chemistry, despite

IUPAC rules, e.g.

Compound ‘common’ name IUPAC name

H3CC

CH3

O

HC

H

O

H3CC

OH

O

H3CO

CH3

Acetone Propanone

Formaldehyde Methanal

Acetic acid Ethanoic acid

Dimethylether Methoxymethane

• Benzene (C6H6) is the simplest aromatic hydrocarbon.

• All C—C bond lengths are equal.

• The resonance description of benzene consists of two

equivalent Lewis structures, each with three double bonds

that alternate with three single bonds.

Benzene

• In benzene, the actual bond length (1.39 Å) is intermediate

between the carbon—carbon single bond (1.53 Å) and the

carbon—carbon double bond (1.34 Å).

Many mono substituted benzenes have common names which you must also learn.

Common Names of Benzene Derivatives

OH OCH3NH2CH3

phenol toluene aniline anisole

C

H

CH2 C

O

CH3

C

O

HC

O

OH

styrene acetophenone benzaldehyde benzoic acid

Methyl phenyl ether

Common Aromatic Compounds

4-Hydroxy-3-methoxybenzaldehyde 2-Acetoxybenzoic acid

2-(Acetyloxy)benzoic acid

2-(4-Isobutylphenyl)propanoic acid

Examples of non-benzene compounds with aromatic

properties are furan, a heterocyclic compound with a

five-membered ring that includes an oxygen atom,

and pyridine, a heterocyclic compound with a six-

membered ring containing one nitrogen atom.