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Question
Define homologous series of organic compounds. List its two characteristics. Write the name and formula of the first member of the series of alkenes.
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Solution
A homologous series is a series of carbon compounds that have different number of carbon atoms but contain the same functional group.
For example, methane, ethane, propane, butane, etc. are all part of the alkane homologous series.
Methane CH4
Ethane CH3CH3
Propane CH3CH2CH3
Butane CH3CH2CH2CH3
There is a difference of −CH2 unit between each successive compound.
Characteristics of homologous series:
All the members of the homologous series have same functional groups and hence similar chemical properties.
Two successive members of a homologous series differ by a −CH2 unit and 14u.
The first member of the series of alkenes in ethene. Its formula is C2H4.
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RELATED QUESTIONS
Write the names and formulae for the first three members of the homologous series for chloroalkanes.
Succeeding members of a homologous series differ by ______.
Give the dot diagram of the first member of the alcohol.
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
Distinguish between homologous organs and analogous organs. In which category would you place wings of a bird and wings of a bat? Justify your answer giving a suitable reason.
The unsaturated hydrocarbons containing a carbon-carbon double bond are called _______.
Find the odd one out and give its explanation.
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 and draw the electron dot structure of first homologue of alkynes series.
Name the third homologue of aldehydes.
