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All questions of Aldehydes, Ketones and Carboxylic Acids for BMAT Exam

The IUPAC name of CH3CHO is:
  • a)
    Acetaldehyde
  • b)
    Ethanal
  • c)
    Formaldehyde
  • d)
    Methanal
Correct answer is option 'A'. Can you explain this answer?

  • The functional group is an aldehyde; −CHO and the given compound has two carbon atoms.
  • Thus, the IUPAC name of the compound is ethanal.

 Which of the following statements are correct in case of the carbonyl bond between carbon and oxygen?
  • a)
    Carbon is the nucleophilic centre and Oxygen is the electrophilic centre.
  • b)
    Oxygen is the nucleophilic centre and Carbon is the electrophilic centre.
  • c)
    Carbon and Oxygen double bond is polarised.
  • d)
    Both ‘b’ and ‘c’ are correct
Correct answer is option 'C'. Can you explain this answer?

Nandini Patel answered
The double bonds in alkenes and double bonds in carbonyl groups are VERY different in terms of reactivity. The C=C is less reactive due to C=O electronegativity attributed to the oxygen and its two lone pairs of electrons.  One pair of the oxygen lone pairs are located in 2s while the other pair are in 2p orbital where its axis is directed perpendicular to the direction of the pi orbitals.  The Carbonyl groups properties are directly tied to its electronic structure as well as geometric positioning.  For example, the electronegativity of oxygen also polarizes the pi bond allowing the single bonded substituent connected to become electron withdrawing.

 Which of the following statement about C=O and C=C is correct?
  • a)
    Both consist of a sigma and pi bond
  • b)
    C=O is polar but C=C is non-polar
  • c)
    Both a and b are correct
  • d)
    Both C=O and C=C undergo nucleophilic addition reactions
Correct answer is option 'C'. Can you explain this answer?

Knowledge Hub answered
  • The first bond formed is a sigma bind and the second one is a pi bond.
  • O has a higher electronegativity than C and hence the electron cloud will be shifted towards the O atom, making the compound polar.
  • This is not possible in C=C.

Propanone and prop-2-en-1-ol are examples of which type of isomerism?
  • a)
    Functional isomers
  • b)
    Chain isomers
  • c)
    Tautomers
  • d)
    Position isomers
Correct answer is option 'A'. Can you explain this answer?

Functional isomers

Explanation: Propanone (CH3COCH3) and prop-2-en-1-ol (CH2=CHCH2OH) are examples of functional isomers because they have the same molecular formula (C3H6O) but different functional groups. Propanone has a carbonyl group (C=O) while prop-2-en-1-ol has an alcohol group (OH) and a carbon-carbon double bond (C=C).

The correct IUPAC name of the folllowing compound is
  • a)
    5,6-Diethyl-8-methyl dec-6-ene
  • b)
    5,7-Diethyl-3-methyl dec-4-ene
  • c)
    5,6-Diethyl-3-methyl dec-4-ene
  • d)
    2,4,5-Triethylnon-3-ene
Correct answer is option 'C'. Can you explain this answer?

Gunjan Lakhani answered
The IUPAC name of the given compound is 5, 6 - diethyl -2- methyldec - 4 - ene. 
The parent hydrocarbon contains 10 carbon atoms and a double bond. 
It is called dec-4-ene.
One methyl group is present on second carbon atom and two ethyl groups are present on fifth and sixth carbon atoms.

What is the common name of 2-methyl-propanal?
  • a)
    formaldehyde
  • b)
    Isobutyraldehyde
  • c)
    carbaldehyde
  • d)
    acetaldehyde
Correct answer is 'B'. Can you explain this answer?

Nikita Singh answered
  • Isobutyraldehyde is the chemical compound with the formula (CH₃)₂CHCHO.
  • It is an aldehyde, isomeric with n-butyraldehyde.
  • Isobutyraldehyde is manufactured, often as a side-product, by the hydroformylation of propene. Its odour is described as that of wet cereal or straw.

Identify the pair of enantiomers amongst the given pairs:
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'B'. Can you explain this answer?

Nandini Iyer answered
The correct answer is Option B.
The 1st option has R configuration and 2nd has S configuration hence they are non super imposable mirror images of each other and are enantiomers.

A hydrocarbon A (C10H18) is capable of showing both enantiomerism as well as diastereomerism. Treatment of A either with HgSO4 / H2SO4 or B2H/ H2O2 -NaOH results in the same carbonyl compound B. Also,
 C can also be obtained as one of the product in the following reaction.
Consider the reaction given below,
Q. 
How many different alcohols are expected?
  • a)
    1
  • b)
    2
  • c)
    3
  • d)
    4
Correct answer is option 'D'. Can you explain this answer?

Compound A has a triple bond and it is symmetrical because its partially reduced product B gives single ozonolysis product C, Also, A shows both enantiomerism and diastereomerism, it must be

As shown above, A has two chiral carbons but simultaneously, it is symmetrical. Hence, it has both meso and a pair of enantiomers as stereoisomers.

Arrange the following compounds in decreasing order of their acid strength: i) trichloroacetic acid ii) trifluoroacetic acid iii) acetic acid and iv) formic acid
  • a)
    trifluoroacetic acid, trichloroacetic acid, formic acid and acetic acid
  • b)
    formic acid., trifluoroacetic acid, trichloroacetic acid, and acetic acid
  • c)
    trichloroacetic acid, trifluoroacetic acid, acetic acid and formic acid.
  • d)
    trifluoroacetic acid, formic acid acetic acid and Propan – 1 – ol, 4 – methylphenol
Correct answer is option 'A'. Can you explain this answer?

Tanuja Kapoor answered
Acidic strength of carboxylic acid -
–  More acidic than phenols or alcohols.
–  Acidity increase with the presence of a group with  -I effect in the alkyl group.Whereas it decreases with the presence of  +I group.
–  Acidity increases with increase in the number of halogen atoms on  - position.
–  It decreases with increasing distance of halogen from   
–  It increases with increase in the electronegativity of halogen.
- CF3COOH > CCl3COOH > HCOOH > CH3 COOH

One mole of a symmetrical alkane on ozonolysis gives two moles of an aldehyde having molecular mass of 44u. The alkene is
  • a)
    Ethene
  • b)
    Propene
  • c)
    1-butene
  • d)
    2-butene
Correct answer is option 'D'. Can you explain this answer?

Priya Patel answered
One mole of a symmetrical alkene on ozonolysis gives two moles of an aldehyde having a molecular weight of mass of 44 u. The alkene is
CH3CH=CHCH3 +O3 ------2CH3CHO
molecular mass of CH3CHO is 12*2+4*1+16 =44
Thus the alkene is 2 butene and the aldehyde formed is ethanal(acetaldehyde)

A strong base can abstract an α – hydrogen from
  • a)
    Alkane.
  • b)
    Amine
  • c)
    Ketone
  • d)
    Alkene
Correct answer is option 'C'. Can you explain this answer?

Vijay Bansal answered
After deprotonation the negative charge will be in conjugation with the pi orbital of carbonyl..so base will prefer to abstract alpha hydrogen from ketone.

In which of the following reactions, ketone is formed as the major organic product?
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'A,C'. Can you explain this answer?

If acid derivatives like nitrile, acid chlorid e or ester is taken in excess in Grignard synthesis, second addition of Grignard’s reagent on carbonyl product does not succeed and carbonyls are obtained as major products.
In option (b), carboxylic acids and in option (d), an aldehyde is formed.

IUPAC name of compound
  • a)
    3-Bromo7-chloro-7ethyl-5-(1,1-dimethyethyl)-5-(2-methylpropyl)-3-methylnonane
  • b)
    3-Bromo7-chloro-5-(1,1-dimethyethyl)-7-ethyl-3methyl-5-(2-methylpropyl)nonane
  • c)
    3-Bromo7-chloro-7ethyl-3-,methyl-5-(1,1-dimethyethyl)-5-(2-methylpropyl)nonane
  • d)
    3-Bromo-5-(1,1-dimethyethyl)-5-(2-methylpropyl)-7-chloro-7ethyl-5--3-methylnonane
Correct answer is option 'B'. Can you explain this answer?

The correct answer is option B
First of all, we should number the carbon atoms from right to left for the above molecule. According to IUPAC rule, we have to name the functional groups alphabetically. Hence, bromine which is attached to 3rd carbon is named as 3-bromo, chlorine which is attached to 7th carbon is named as 7-chloro and ethyl group which is also attached to 7th carbon is named as 7-ethyl. 5-(1,1-dimethyethyl) indicates that, 2 methyl groups are attached to the 1st carbon of ethyl group which is attached to the 5th carbon of the given molecule. 5-(2-methylpropyl) indicates that, a methyl group is attached to the 2nd carbon of propyl group which is attached to the 5th carbon of the given molecule. Finally, since the molecule has nine atoms and it is an alkane, the word nonane is added to the IUPAC name.
 

How manyh assymmetric carbon atoms are present in
(i) 2-Dimethyl cyclohexane
(ii) 3-Methyl cyclopentene
(iii) 3-Methylcyclohexene
  • a)
    2,1,1
  • b)
    1,1,1
  • c)
    2,0.2
  • d)
    2,0,1
Correct answer is option 'A'. Can you explain this answer?

Aarya Khanna answered
Asymmetric carbon atoms are those carbon atoms which are attached to four different groups or atoms. These carbon atoms are also known as chiral centers.

(i) 2-Dimethyl cyclohexane:
- Cyclohexane has no asymmetric carbon atoms.
- When two methyl groups are attached to cyclohexane, it becomes 2,3-dimethyl cyclohexane.
- The carbon at position 2 is attached to two methyl groups and two hydrogen atoms. Therefore, it is not an asymmetric carbon atom.
- The carbon at position 3 is attached to one methyl group, one hydrogen atom, one methyl group, and one cyclohexane ring. Therefore, it is an asymmetric carbon atom.
- Hence, there is one asymmetric carbon atom in 2-dimethyl cyclohexane.

(ii) 3-Methyl cyclopentene:
- Cyclopentene has one asymmetric carbon atom.
- When a methyl group is attached to cyclopentene at position 3, it becomes 3-methyl cyclopentene.
- The carbon at position 3 is attached to one methyl group, one hydrogen atom, one double bond with carbon, and one cyclopentene ring. Therefore, it is an asymmetric carbon atom.
- Hence, there is one asymmetric carbon atom in 3-methyl cyclopentene.

(iii) 3-Methylcyclohexene:
- Cyclohexene has one asymmetric carbon atom.
- When a methyl group is attached to cyclohexene at position 3, it becomes 3-methylcyclohexene.
- The carbon at position 3 is attached to one methyl group, one hydrogen atom, one double bond with carbon, and one cyclohexene ring. Therefore, it is an asymmetric carbon atom.
- Hence, there is one asymmetric carbon atom in 3-methylcyclohexene.

Therefore, the correct answer is option 'A' (2,1,1) as there are 2 asymmetric carbon atoms in total, with 1 in 2-dimethyl cyclohexane, 1 in 3-methyl cyclopentene, and 1 in 3-methylcyclohexene.

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