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प्रश्न
What is a homologous series?
What is a homologous series? Explain with an example.
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उत्तर १
Homologous series is a group of organic compounds with a similar structure and similar chemical properties in which the successive compounds differ by a CH2 group.
उत्तर २
A homologous series is a series of carbon compounds that have different numbers of carbon atoms but contain the same functional group.
For example, methane, ethane, propane, butane, etc. are all part of the alkane homologous series. The general formula of this series is CnH2n+2.
Methane CH4
Ethane CH3CH3
Propane CH3CH2CH3
Butane CH3CH2CH2CH3
It can be noticed that there is a difference of -CH2 unit between each successive compound.
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संबंधित प्रश्न
Write the next homologue of the following: C2H4
Write the next homologue of the following: C4H6
Write the names and formulae for the first three members of the homologous series for chloroalkanes.
Define a homologous series. Give the name and structural formula of one homologue of the following:
CH3OH
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.
A colourless organic liquid X of molecular formula C2H4O2 turns blue litmus to red. Another colourless organic liquid Y of molecular formula C3H6O has no action on any litmus but it is used as a nail polish remover. A yet another colourless organic liquid Z of molecular formula C2H6O has also no action on litmus but it is used in tincture of iodine.
(a) Name the liquid X. To which homologous series does it belong? Give the name of another member of this homologous series.
(b) Name the liquid Y. To which homologous series does it belong? Write the name of another member of this homologous series.
(c) Can you name an organic compound having the same molecular formula as liquid Y but which belongs to a different homologous series? What is this homologous series?
(d) Name the liquid Z. To which homologous series does it belong? Write the name of another member of this homologous series.
Succeeding members of a homologous series differ by ______.
Give the dot diagram of the first member of the alcohol.
What is the difference in the molecular formula of any two adjacent homologues in terms of molecular mass?
Study the different conclusions drawn by students of a class on the basis of observations of preserved/available specimens of plants and animals.
I. Potato and sweet potato are analogous organs in plants.
II. Wings of insects and wings of birds are homologous organs in animals.
III. Wings of insects and wings of bats are analogous organs in animals.
IV. Thorns of citrus and tendrils of cucurbita are analogous organs in plants.
The correct conclusions are:
(A) I, and II
(B) II and IV
(C) I and III
(D) III and IV
As one ascends in any homologous series, physical properties change gradually.
There are different general molecular formula for all members of the homologous series.
Write a short note.
Homologous series
Complete the following table for homologous series of Alkenes.
| Name | Molecular formula | Condensed structural formula | Number of carbon atom | Number of -CH2- units | Boiling point °C |
| Ethene | C2H4 | CH2 = CH2 | 2 | 0 | -102 |
| Propene | C3H6 | CH3–CH = CH2 | 3 | 1 | -48 |
| 1-Butene | C4H8 | CH3–CH2–CH = CH2 | ______ | ______ | -6.5 |
| 1-Pentene | C5H10 | CH3–CH2–CH2–CH = CH2 | ______ | ______ | 30 |
Observe the structural formula and answer the following questions.
- Write the name of the given hydrocarbon.
- The given hydrocarbon is included in which type of hydrocarbon?
- What is the kind of compounds with the above characteristic structure called?
Complete the following chart by using examples given in brackets.
(isobutylene, cyclohexane, propane, cyclohexene, cyclopentane, benzene, propyne, isobutane, propene)
| Straight chain hydrocarbons | Branched chain hydrocarbons | Cyclic hydrocarbons |
What is called homologous series? Give any three of its characteristics?
Name and draw the electron dot structure of first homologue of alkynes series.
Name the third homologue of aldehydes.
