Test: Structural Isomerism- 1

18 Questions MCQ Test Chemistry for JEE | Test: Structural Isomerism- 1

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Direction (Q. Nos. 1-18) This section contains 18 multiple choice questions. Each question has four
 choices (a), (b), (c) and (d), out of which ONLY ONE option is correct.


How many diffrent alkenes exist for C5H10 which are structural isomeres ?



 Two times double bond can’t appear as it has asked alkene and not alkadiene. So, these are the only types of alkenes that can be formed which are structural isomers.


The molecular formula C5H12 contains how many isomeric alkanes?


n-pentane, 2-ethylpropane, and 2-methylbutane are the 3 isomeric alkanes of C5H12 (pentane).


How many cycloalkene isomers exist for C5H8 which contain at least one methyl locant directly present on the ring? 


These are the only cases in which a methyl group can be added on a cycloalkene.


 Which of the following compounds will exhibit cis-trans isomerism? 


The compounds with each doubly bonded carbon attached to two different groups (like Cab=Cab, Cab=Ccd) exhibit geometrical isomerism i.e., cis and trans forms. The geometrical isomerism arises due to restricted rotation of double bond.

However, even though there is restricted rotation for triple bond, alkynes do not exhibit geometrical isomerism, since the triply bonded carbons are attached to one group each only.


How many structural isomers exist for C4 H80 which are simultaneously ether? Also there is no atom sp2-hybridised. 


Correct Answer :- D

Explanation :


Organic compound with molecular formula C4H8O2 cannot have the functional group


Double bond equivalent of the given compound C4H8O2 is 1. So we will have compounds that have either a double bond or a ring. In option c, we have dialdehyde which is a 2 double bond compound. So it is not possible.


How many structural isomers are possible with molecular formula C4H10O ?


The formula that these isomers contain no rings or double bonds. The isomers must be alcohols and ethers.
For The alcohols
1. CH3CH2CH2CH2OH, butan 1-ol
2. CH3CH2CH(OH)CH3, butan-2-ol
3. (CH3)2CHCH2OH, 2-methylpropan-1-ol 
4. (CH3)3COH, 2-methylpropan-2-ol.
Now for the ethers.
5. CH3CH2CH2OCH3, 1-methoxypropane
6. CH3CH2OCH2CH3 , ethoxyethane
7. (CH3)2CHOCH3 , 2-methoxypropane.


How many structural isomers are possible for compounds containing C, H and O atoms only with their molar masses 100 as well as the isomers are simultaneously ketones ?


General formula of ketone = CnH2nO
12x+2x+16 = 100
x = 6
So, the formula of compound is C6H12O. We have to make ketone only. These are as follow


For which of the following parameters the structural isomers C2H5OH and CH3OCH3 would be expected to have the same values?

[AIEEE 2004]


Vapor density = Molecular weight/2

As both the compounds have same molecular weights, both will have the same vapour density. Hence, gaseous density of both ethanol and dimethyl ether would be same under identical conditions of temperature and pressure. The rest of these three properties; Vapour pressure, boiling point and heat of vaporization will differ as ethanol has hydrogen bonding whereas ether does not.


Compounds which have same molecular formula but different structural formula is called


Tert butyl chloride will have mass in decimals (since Cl is its constituent and it has fractional mass), so it will not be considered. In Iso hexane there are 5 different positions, so we can’t get one single monosubstituted alkyl halide.
In neo-hexane, we have 3 different positions for mono substitution, so we can’t get one single monosubstituted alkyl halide.
However in neopentane, we have a single position for substitution. So we can get one single monosubstituted alkyl halide.


A monocarboxylic acid is a functional isomer os 

[JEE Main 2013 Online Exam]


 In ethers, alcohols and amines, there is no double bond. However, esters have one double bond as same as monocarboxylic acid. So monocarboxylic  acid is a functional isomer of ester (only for no. of carbon greater than 2. As we need to have at least 3 carbon atoms to form ester.)


In allene (C3H4 ), the type(s) of hybridisation of the carbon atoms is (are) 

[JEE Main 2014 Online Exam]


Which of the following statements are correct?

I. A pair of positional isomers differs in the position of the same functional group.
II. A pair of. structural isomers have the same relative molar mass.
Ill. A pair of functional group isomers belongs to different homologous series. 


According to me all statements are correct. For statement I, positional isomers have the same functional group. They just differ in the position of that group.
Statenmen II- Structural isomers have the same relative molar mass. Actually relative mass means the mass of one isomer is samee relative to another. Structural isomers differ in the structure of molecules. However they have the same molecular formula and hence; same molar mass.
Statement III- According to me, this statement is correct. As homologous series must contain the same functional group with the same physical & chemical properties. Also functional group isomers differ in the functional group attached with them. So, functional group isomers belong to different homologous series. ​


Which of the following statements regarding ethanoic acid and methyl methanoate are correct?
I. They are functional group isomers with molecular fo nula C2H4O2.
II. They belong to different homologous series.
Ill. They have different chemical properties. 


Methyl methanoate and ethanoic acid are functional group isomers as they have the same molecular formula but the connectivity differs.
Since they have different functional groups, they belong to different homologous series.
Different homologous series have different properties.


Which of the following statements concerning 3,4-dibromo-1-pentene and 3,5-dibromo-2-pentene are correct?
(I) They have same molecular formula C5H8Br2
(II) They are positional isomers.
(III) They have similar chemical properties.


They are positional isomers, hence same molecular formula C5H8Br2. However, they are structure isomers, hence different physical and chemical properties.


How many structurral isomers C4H8 have ?


C4H8 structural isomers are as follow:-

But we need structural isomers. So structure 2 and 3 will be a single entity. Hence we have 4 structural isomer in all.


Which of the following compounds are structural isomers of C5H10O?

I. 2-methyl butanal
II. Propyl ethanoate
Ill. Pentanal 


Double bond equivalent of C5H10O is 1. So, it will have either a double bond or a ring.So, it may be an aldehyde, ketone, alcohol( carbon chain having double bond) or epoxide.
Propyl ethanoate has 2 oxygen atoms. So, it will never be its isomer. HOwever option a and c will be its isomer as they are aldehyde.


Constitutional isomerism is possible in alkenes only if the number of carbon atoms present is 


The reason behind this is that only for no. of carbon atoms greater or equal to 4, we can make different chains or rings. So, the answer is a

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