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Question
Name the following organic compound:
The first homologue whose general formula is CnH2n.
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Solution
Ethene
Explanation:
CnH2n is the general formula for the homologous series of alkenes. The first member of the alkene family is the compound having two carbon atoms which are known as ethene. Methene is not possible as at least two carbons are required for the formation of the double bond.
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RELATED QUESTIONS
Write the name and formula of the 2nd member of homologous series having general formula CnH2n – 2.
What is the difference between two consecutive homologues:
(1) in terms of molecular mass?
(2) in terms of number and kind of atoms per molecule?
By how many carbon atoms and hydrogen atoms do any two adjacent homologues differ?
The molecular formula of a homologue of butane is:
(a) C4H8
(b) C3H6
(c) C4H6
(d) C3H8
The molecular formula of the third member of the homologous series of ketones is:
(a) C4H8O
(b) C3H6O
(c) C5H10O
(d) C6H12O
An organic compound having the molecular formula C3H6O can exist in the form of two isomers A and B having different functional groups. The isomer A is a liquid which is used as a solvent for nail polish. The isomer B is also a liquid. An aqueous solution of one of the lower homologues of B is used for preserving biological specimens in the laboratory
(a) What is compound A?
(b) Write the electron-dot structure of A.
(c) What is compound B?
(d) Write the electron-dot structure of B.
(e) Name the lower homologue of compound B which is used in preserving biological specimens.
What is the difference in the molecular formula of any two adjacent homologues in terms of molecular mass?
Write names of first four homologous series of alcohols.
Complete the following table for homologous series of alcohols.
| Name | Molecular formula | Condensed structural formula | Number of carbon atom | Number of -CH2- units | Boiling point °C |
| Methanol | CH4O | CH3-OH | 1 | 1 | 63 |
| Ethanol | C2H6O | CH3–CH2-OH | 2 | 2 | 78 |
| Propanol | C3H8O | CH3–CH2–CH2-OH | ______ | ______ | 97 |
| Butanol | C4H10O | CH3–CH2–CH2–CH2–OH | ______ | ______ | 118 |
Name the third homologue of alcohols.
