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Question
Define a homologous series. Give the name and structural formula of one homologue of the following:
CH3OH
Solution
Homologous series: A series of organic compounds having similar structures and chemical properties and in which the successive compounds differ by -CH2 group is called a homologous series. A homologue of CH3OH will differ by the -CH2 group; therefore, methanol's successive homologue will be ethanol (C2H5OH).
The structural formula of ethanol is as follows:
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RELATED QUESTIONS
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?
Give the molecular formula of one homologue of each of the following:
C2H6
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?
Two statements are given - one labeled Assertion (A) and the other labeled Reason (R).
Assertion (A): In a homologous series of alcohols, the formula for the second member is C2H5OH and the third member is C3H7OH.
Reason (R): The difference between the molecular masses of the two consecutive members of a homologous series is 144.
Saturated hydrocarbon : Single bond : : Unsaturated hydrocarbon : _______
Complete the following table for the homologous series of alkanes.
| Name | Molecular formula | Condensed structural formula | Number of carbon atom | Number of -CH2- units | Boiling point °C |
| Methane | CH4 | CH4 | 1 | 1 | -162 |
| Ethane | C2H6 | CH3–CH3 | 2 | 2 | -88.5 |
| Propane | C3H8 | CH3–CH2–CH3 | 3 | 3 | -42 |
| Butane | C4H10 | CH3–CH2–CH2–CH3 | ______ | ______ | 0 |
| Pentane | C5H12 | CH3–CH2–CH2–CH2–CH3 | ______ | ______ | 36 |
| Hexane | C6H14 | CH3–CH2–CH2–CH2–CH2–CH3 | ______ | ______ | 69 |
Which of the following pairs can be the successive members of a homologous series?
Name the following:
Group of organic compounds where the successive members follow a regular structural pattern, successive compounds differ by a 'CH2' group.
