CARBON AND ITS COMPOUNDS -2
Some functional groups in carbon compounds
● Carbon also forms bonds with other elements such as halogens, oxygen, nitrogen and
sulphur. In a hydrocarbon chain, one or more hydrogens can be replaced by these
elements, such that the valency of carbon remains satisfied.
● In such compounds, the element replacing hydrogen is referred to as a heteroatom.
● These heteroatoms and the group containing these confer specific properties to the
compound, regardless of the length and nature of the carbon chain and hence are
called functional groups.
HOMOLOGOUS SERIES
Homologous series is a group of organic compounds having similar structures and similar
chemical properties in which the successive compounds differ by CH2 group.
CHARACTERISTICS OF A HOMOLOGOUS SERIES
1. All the members of a homologous series can be represented by the same general
formula.
2. Any two adjacent homologues differ by 1 carbon atom and 2 hydrogen atoms in their
molecular formulae. CH4 and C2H6 — these differ by a –CH2- unit
C2H6 and C3H8 — these differ by a –CH2- unit
3. The difference in the molecular masses of any two adjacent homologues is 14u. Eg
CH4 - 16u & C2H6 - 30u (30-16 = 14u)
4. All the compounds of a homologous series show similar chemical properties.
5. The members of a homologous series show a gradual change in their physical
properties with increase in molecular mass.
Try this out:
Calculate the difference in the formulae and molecular masses for (a) CH3OH and C2H5OH
(b) C2H5OH and C3H7OH, and (c) C3H7OH and C4H9OH.
IUPAC naming of hydrocarbons:
1) The IUPAC system is a systematic nomenclature in which the name of a compound
correlates to its molecular structure.
2) The IUPAC nomenclature system is a set of logical rules devised and used to write a
unique name for every distinct compound. According to the IUPAC system of
nomenclature, the name of an organic compound consists of a root word, a suffix and
a prefix.
Suffix:
A suffix designates the functional groups that may be present in the compound. The suffix is
again divided into primary and secondary.
Primary suffix:
Primary suffix indicates the degree of saturation or unsaturation in the basic skeleton and is
added immediately after the root word. (ane, ene, yen)
Root word + primary suffix→ Saturated or unsaturated carbon chain
Secondary suffix:
Secondary suffix indicates the presence of a functional group attached with the hydrocarbon
chain. (Eg., aldehyde - al, alcohol - ol, ketone - one, acid - oic)
Nomenclature of Alkanes:
For saturated hydrocarbons, the primary suffix “ane” should be added.
Example: The IUPAC name of a molecule which contains single bond between carbon atoms.
CH3-CH3 : Eth + ane : Ethane
CH3-CH2-CH3 : Prop + ane : Propane
Nomenclature of Alkenes:
Hydrocarbons containing double bonds are known as alkenes. For such hydrocarbons, the
primary suffix “ene” should be added to the root word.
Example: The IUPAC name of a molecule which contains a double bond between carbon
atoms.
CH2=CH2: Eth + ene: Ethene
CH3-CH=CH2: Prop + ene: Propene
Example:
CH2=CH-CH2-CH3:
Root word: But
Suffix- ene
Root word suffix: Butene
Nomenclature of Alkynes:
Hydrocarbons that contain a triple bond between carbon atoms are known as alkynes and for
naming such hydrocarbons the primary suffix “yne “should be added.
Example: The IUPAC name of a molecule which contains a triple bond between carbon
atoms.
CH≡CH: Eth + yne: Ethyne
CH3-C≡CH: Prop + yne: Propyne
In writing nomenclature of alkynes according to IUPAC, it is important to mention the
position of triple bond for the molecules which contain more than three carbon atoms.
Example:
CH≡C-CH2-CH2-CH3:
Root word: Pent
Suffix : yne
Root word + suffix: Pentyne
CH3-C≡C-CH2-CH2-CH3
Root word: hex
Suffix: yne
Root word + suffix: hexyne
Secondary Suffix:
A secondary suffix indicates the functional group present in the carbon compound. Functional
groups are defined as specific atoms, groups of atoms or ions which are part of a larger
hydrocarbon chain and impart characteristic properties to the compounds.
CH3-CH2-CHO :
Root word:Prop
Primary suffix: an
Secondary suffix: al
Root word + Primary suffix + Secondary suffix: Propanal
CH3-CH2-OH : Eth +an +ol : Ethanol
PREFIX:
CH3-CH2-CH2-Cl
Root word: Prop
Primary suffix: ane
Prefix: Chloro
Prefix + Root word + primary suffix: Chloro propane
CH3-CH2-Cl
Root word: Eth
Primary suffix: ane
Prefix: Chloro
Prefix + Root word + primary suffix: Chloro ethane
