All questions of Organic Chemistry — Some Basic Principles & Technique for JEE Exam

Among the following, the molecule with the highest dipole moment is:
  • a)
    CH3Cl
  • b)
    CH2Cl2
  • c)
    CHCl3
  • d)
    CCl4
Correct answer is option 'A'. Can you explain this answer?

Nandita Chopra answered
NOTE : Dipole moment is a vector quantity.
Methane molecule being symmetrical, has zero dipole moment. Replacement of one of the H– atoms by Cl atom increases the dipole moment. The increase in dipole moment is rather more than what can be expected because of the fact that the bond dipole moment of C – H bond and that of C – Cl bond reinforce one another.
Replacement of another H atom by Cl increases the bond angle due to lone pair – lone pair repulsion between two Cl–atoms thereby reducing the dipole moment of the molecule.  Increase in angle is again caused by the the introduction of the third Cl–atom.
When the fourth Cl–atom is introduced, the molecule (CCl4) again becomes symmetrical and dipole moment reduces to zero. So, CH3Cl will have the maximum dipole moment.

The compound which gives the most stable carbonium ion on dehydration is :
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'B'. Can you explain this answer?

Rohit Jain answered
NOTE : The order of stability of carbonium ion is
tertiary > secondary > primary > methyl
Tertiary carbonium ions (formed in b) are more stable because of electron repelling (+I effect) nature of CH3 group due to which the +ve charge gets dispersed and also due to hyperconjugation.

The number of isomers of C6H14 is 
  • a)
    4
  • b)
    5
  • c)
    6
  • d)
    7
Correct answer is option 'B'. Can you explain this answer?

1) N-hexane
2)2 ,Methyl pentane
3)2,2 dimethyl butane
4)2,3 dimethyl butane
5)3 methyl pentane

In the following carbocation, H/CH3 that is most likely to migrate to the positively charged carbon is
  • a)
    CH3 at C-4
  • b)
    H at C-4
  • c)
    CH3 at C-2
  • d)
    H at C-2
Correct answer is option 'D'. Can you explain this answer?

Akash Kumar answered
As we know that the migratory aptitude of H-ion is more than CH3- ion.And we always have to form the most stable carbocation in case of rearrangement. Hence if we remove H-Ion form C4 linkage we will gate a +ve charge in the vicinity of a lone pair which is very stable due to back bonding.So option D is correct. I hope u get it.

Among the following, the compound that can be most readily sulphonated is
  • a)
    benzene
  • b)
    nitrobenzene
  • c)
    toluene
  • d)
    chlorobenzene
Correct answer is option 'C'. Can you explain this answer?

TIPS/FORMULAE :
–NO2, –Cl and –OH are electron-attracting or withdrawing group due to –M, –E and/or –I effects where as –CH3 show, +I effect (electron releasing).
Because of the + I effect of the CH3 group, toluene has the highest electron density in the o- and p- positions and hence can be most readily sulphonated.

The alkene that exhibits geometrical isomerism is:
  • a)
    2- methyl propene 
  • b)
    2-butene
  • c)
    2- methyl -2- butene
  • d)
    pr open e
Correct answer is option 'B'. Can you explain this answer?

Sahana Joshi answered
Correct answer is option (B) : 2-butene
When two groups attached to a double bonded carbon atom are same, the compound does not exhibit geometrical isomerism.
Compounds in which the two groups attached to a double bonded carbon are different, exhibit geometrical isomerism, thus, only 2-butene exhibits cis-trans isomerism.

The Cl—C—Cl angle in 1,1,2,2-tetrachloroethene and tetrachloromethane respectively will be about 
  • a)
    120º and 109.5º
  • b)
    90º and 109.5º
  • c)
    109.5º and 90º
  • d)
    109.5º and 120º
Correct answer is option 'A'. Can you explain this answer?

The bond angle in sp3, sp2 and sp hybridization is respectively 109.28', 120º and 180º.
Tetrachloroethene being an alkene has sp2 hybridised C-atoms and hence the Cl – C –  Cl angle is 120º, whereas in tetrachloromethane, carbon is sp3 hybridised, so the angle is 109º.28’.

Arrangement of (CH3)3C –, (CH3)2CH –, CH3 – CH2 – when attached to benzyl or an unsaturated group in increasing order of inductive effect is
  • a)
    (CH3)3C – < (CH3)2CH – < CH3 – CH2
  • b)
    CH3 –CH2– < (CH3)2 CH – < (CH3)3C –
  • c)
    (CH3)2CH– <(CH3)3C –< CH3, –CH2
  • d)
    (CH3)3C– < CH3 –CH2 –(CH3)2CH –
Correct answer is option 'B'. Can you explain this answer?

Hyperconjugation effect increases in the order :
(CH3)3C−<(CH3)2CH−<CH3CH2−
The σ electrons of C—H bond of the alkyl group enter into partial conjugation with the attached unsaturated system or with the unshared p orbital.
Hence (B) is the correct answer.

Which of the following represents the given mode of hybridisation sp2 – sp2 – sp – sp from left to right?
  • a)
    H2C = CH – C ≡ N
  • b)
    HC ≡ C – C ≡ CH
  • c)
    H2C = C = C = CH2
  • d)
Correct answer is option 'A'. Can you explain this answer?

Notes Wala answered
A has the following hybridization order:
Nitrogen atom has an sp hybridization because it has three bond pairs and one lone pair.
Note: lone pair and negative charge on an atom can be converted to a bond while considering the hybridization.
B has the following hybridization order:
C has the following hybridization order:
D has the following hybridization order:
Hence A is the correct answer.

An SN2 reaction at an asymmetric carbon of a compound always gives
  • a)
    an enantiomer of the substrate
  • b)
    a product with opposite optical rotation
  • c)
    a mixture of diastereomers
  • d)
    a single stereoisomer
Correct answer is option 'D'. Can you explain this answer?

Manisha Mehta answered
SN2 reactions proceed with inversion of configuration.
Since the attacking nucleophile is not necessarily the same as that of leaving group, the product cannot be enantiomer of the substrate and thus necessarily will not have opposite optical rotation. Moreover since only one product is obtained, we can not obtain diastereomers.

Due to the presence of an unpaired electron, free radicals are:
  • a)
    cations
  • b)
    an ions
  • c)
    chemically inactive
  • d)
    chemically reactive
Correct answer is option 'D'. Can you explain this answer?

Mohit Patel answered
(D) :- Free radicals are highly reactive due to presence of an unpaired electron. They readily try to pairup the odd electrons.

The bond order of in dividual carbon -carbon bonds in benzene is
  • a)
    one
  • b)
    two
  • c)
    between one and two
  • d)
    one and two, alternately
Correct answer is option 'C'. Can you explain this answer?

Pranav Pillai answered
NOTE : The phenomenon of resonance gives identical bonding and hence identical bond lengths.
C – C bond order in benzene = 1.5

The products of combustion of an aliphatic thiol (RSH) at 298 K are
  • a)
    CO2(g), H2O(g) and SO2(g)
  • b)
    CO2(g), H2O(l) and SO2(g)
  • c)
    CO2(l), H2O(l) and SO2(g)
  • d)
    CO2(g), H2O(l) and SO2(l)
Correct answer is option 'B'. Can you explain this answer?

Deepika Das answered
Products of Combustion of Aliphatic Thiol (RSH)
The combustion of an aliphatic thiol (RSH) typically results in the formation of several products. In this case, the products are:

CO2(g), H2O(l) and SO2(g)
Here's why:
- CO2(g): Carbon dioxide is a common product of combustion reactions involving organic compounds. It is formed when the carbon in the aliphatic thiol combines with oxygen during combustion.
- H2O(l): Water is also a common product of combustion reactions. In this case, the hydrogen in the aliphatic thiol combines with oxygen to form water.
- SO2(g): Sulfur dioxide is produced when sulfur in the aliphatic thiol combines with oxygen during combustion. It is a common product of combustion reactions involving sulfur-containing compounds.
Therefore, the correct combination of products for the combustion of an aliphatic thiol at 298 K is CO2(g), H2O(l), and SO2(g) as given in option B.

Which of the following acids has the smallest dissociation constant ?
  • a)
    CH3CHFCOOH
  • b)
    FCH2CH2COOH
  • c)
    BrCH2CH2COOH
  • d)
    CH3CHBrCOOH
Correct answer is option 'C'. Can you explain this answer?

Tejas Chawla answered
TIPS/Formulae :
(i) The inductive effect decreases with increase in distance of halogen atom from the carboxylic group and hence the strength of acid proportionally decreases.
(ii) Th e acidity in cr eas es with th e in cr eas e in electronegativity of the halogen present.
Smallest dissociation constant means weakest acid, which is BrCH2 CH2COOH because here Br (less electronegative than F) is two carbon atoms away from – COOH.

The alkene formed as a major product in the above elimination reaction is
  • a)
  • b)
  • c)
  • d)
    CH2 = CH2
Correct answer is option 'B'. Can you explain this answer?

Vivek answered
See, in this one, HYPERCONJUGATION will decide the major product. Hyperconjugation is dependent on the number of α-H's. See the carbon to which Me is attached. Check the number of H's α to this carbon in each option. The one with the max number of them will be the major product. It's B.

In the compound CH2 = CH–CH2–CH2–C ≡ CH, the C2–C3 bond is of the type,
  • a)
    sp – sp2
  • b)
    sp3 – sp3
  • c)
    sp – sp3
  • d)
    sp2 – sp3
Correct answer is option 'D'. Can you explain this answer?

Kaavya Pillai answered
The compound CH2=CH is known as ethene or ethylene. It is an organic compound with the formula C2H4. Ethene is a colorless gas with a sweet odor and is commonly used in the production of plastics, solvents, and as a fuel.

Among the following compounds, the most acidic is
  • a)
    p-nitrophenol
  • b)
    p-hydroxybenzoic acid
  • c)
    o-hydroxybenzoic acid
  • d)
    p-toluic acid
Correct answer is option 'C'. Can you explain this answer?

Mira Sharma answered
will be most acidic due to hydrogen bonding .among B) and D) ...B) will be more acidic as -OH is slighlty e- withdrawing 
so correct order should be - (C) o-hydroxybenzoic > (B) p-hydroxybenzoic > (D) p-toluic acid > (A) p-nitrophenol 

Which of the following compounds will exhibit geometrical isomerism ?
  • a)
    2 - Phenyl -1 - butene
  • b)
    1, 1 - Diphenyl - 1 - propene
  • c)
    1 - Phenyl - 2 - butene
  • d)
    3 - Phenyl -1 - butene
Correct answer is option 'C'. Can you explain this answer?

Correct answer is option C: 1-phenyl-2-butene
1. Alkene in which different groups are attached with the double bonded carbon atoms, exhibit geometrical isomerism.
2. Alkene in which different groups are attached with the double bonded carbon atoms, exhibit geometrical isomerism.

The general formula CnH2nO2 could be for open chain
  • a)
    carboxylic acids
  • b)
    diols
  • c)
    dialdeh ydes
  • d)
    diketon es
Correct answer is option 'A'. Can you explain this answer?

Maulik Khanna answered
General formula CnH2nO2 for carboxylic acids

Carboxylic acids are a class of organic compounds that contain the carboxyl functional group (-COOH). The general formula for carboxylic acids is CnH2nO2, where 'n' represents the number of carbon atoms in the carbon chain.

Explanation:
Carboxylic acids are organic compounds that contain a carboxyl functional group (-COOH) attached to a carbon atom. This functional group consists of a carbonyl group (C=O) and a hydroxyl group (OH) bonded to the same carbon atom. The carbon atom is also bonded to an alkyl or aryl group.

The general formula CnH2nO2 represents the molecular formula of carboxylic acids. The 'n' in this formula represents the number of carbon atoms in the carbon chain. For example, if 'n' is 1, the formula becomes CH3COOH, which is the molecular formula for acetic acid.

Carboxylic acids can have both linear and branched carbon chains. The carbon chain can contain various functional groups and substituents, but the carboxyl group remains the characteristic functional group of carboxylic acids.

Examples:
1. Methanoic acid (formic acid) - CH2O2
2. Ethanoic acid (acetic acid) - C2H4O2
3. Propanoic acid - C3H6O2
4. Butanoic acid - C4H8O2

The general formula CnH2nO2 allows us to determine the molecular formula of any carboxylic acid based on the number of carbon atoms present in the carbon chain. This formula helps in identifying and classifying carboxylic acids based on their molecular composition.

Therefore, the correct answer is option 'A' - carboxylic acids.

Which of the following is the strongest base ?
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'D'. Can you explain this answer?

Anaya Patel answered
Lone pair of electrons present on the  nitrogen of  benzyl amine is not involved  in resonance

Among the following four structures I to IV,

it is true that
  • a)
    only I and II are chiral compounds
  • b)
    only III is a chiral compound
  • c)
    only II and IV are chiral compounds
  • d)
    all four are chiral compounds
Correct answer is option 'A'. Can you explain this answer?

Sarika Bharti answered
Option 'A' is correct because in compound I the carbon has all the 4 different or non identical groups. Similarly in compound II while compound III have 3 H atoms which is identical and similarly in compound IV the carbon atom have 2 ethyl group. That's why the correct option is 3.

In CH3CH2OH, the bond that undergoes heterolytic cleavage most readily is
  • a)
    C—C
  • b)
    C—O
  • c)
    C—H
  • d)
    O—H
Correct answer is option 'D'. Can you explain this answer?

Vivek answered
Due to high difference in electronegativity, polarity of the bond is high. So it's easier to break C—O bond.

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