31 Year NEET Previous Year Questions: Some Basic Principles & Techniques - 1 - NEET MCQ

Alkenes with double bonds cannot undergo free rotation and can have different geometrical shapes with two different groups on each end of the double bond.

Explanation: Presence of three — NO2 groups in o–, p– positions to phenolic groups (in III) makes phenol strongly acidic because its corresponding phenolate ion (conjugate base) is highly stabilized due to resonance.

Conjugate base of CH3COOH, (II) (i.e.CH3COO-) is a resonance hybrid of two equivalent structures.

The conjugate base of phenol, (IV) is stabilized due to resonance note that here all resonating structures are not equivalent).

The conjugate base of cyclohexanol, (I) does not exhibit resonance, hence not formed.

Hence A is the correct answer.

Tertiary alkyl halide is most reactive towards nucleophilic substitution because the corresponding carbocation (3°) is most stable. Aryl halide is least reactive due to partial double bond character of the C – Cl bond.

Presence of — NO₂ groups in ortho and para positions  increases the reactivity of the – Cl towards nucleophiles.

Cl^– is the weakest base and hence better leaving group

Due to +M+M effect of −OH-OH group and hyperconjugation of −CH3-CH3 group.

The bulky methyl groups are maximum away from each other.

Due to hydrogen bonding between the two OH groups, gauche conformation of ethylene glycol (a) is the most stable conformation.

has a lone pair of electrons on oxygen atom, thus not an electrophile. Also octet is complete.

Due to +M effect of –OH group and hyperconjugation of –CH₃ group.

Both methyl and hydroxyl groups are electron releasing groups hence +I effect increases. Therefore B will be most reactive in an electrophilic reaction.

Hence B is correct.

The given compound is

4 ethyl, 3 propyl hex – 1 – ene

Bond length order is

Because of high electronegativities of the halogen atom, the carbon halogen (C – X) is highly polarised covalent bond. Thus, the carbon atom of the C – X bond becomes a good site for attack by nucleophiles (electron rich species). Nucleophilic substitution reactions are the most common reactions of alkyl halides.

In S_NAr reactions, a carbanion is formed as an intermediate, so any substituent that increases the stability of carbanion and hence the transition state leading to its formation will enhance the S_NAr reactions. To compare the rates of substitution in chlorobenzene, chlorobenzene having electron-withdrawing group, and chlorobenzene having electronreleasing group, we compare the structures carbanion I (from chlorobenzene), II (from chlorobenzene containing electron-withdrawing group) and III (from chlorobenzene containing electron-releasing group).

G withdraws electrons, neutralises (disperses) –ve charge of the ring, stabilises carbanion, facilitates S_N reaction (activation effect)

G releases electrons, intensifies –ve charge, destabilizes carbanion, retards S_N reaction (deactivation) NO₂ is activating group and CH₃ and OCH₃ are deactiving group.
Hence, the correct order of nucleophilic substitution reactions

Correct IUPAC name of above compound is trans-2-chloro-3-iodo-2-pentene

Given wt of compound taken (w) = 0.35 g
Volume of nitrogen collected (V) = 55 ml
Room temperature (t K) = 300 K
Atmospheric pressure (P) = 715 mm Aq. tension (ρ) = 15 mm
Calculation -Volume of N₂ at NTP

% of nitrogen

Conc. HNO₃ decomposes NaCN and Na₂S to avoid their interference.

Electrophilic rate order

Since nitration is an electrophilic substitution hence presence of electron releasing group like CH₃ in the nucleus facilitates nitration.

In IUPAC system of nomenclature, preference is given to multiple bond than halogen substituent, so the correct name of

 is 3-Bromoprop-1-ene.

It shows geometrical isomerism but does not show optical isomerism.

IUPAC name of the structure is 3-ethyl-2-hydroxy-4-methylhex-3-en-5-ynoic acid

Decreasing order of deactivating effect of the given  m-directing group is > NO₂ > – CN > – SO₃H > – COOH
—NO₂ group is most deactivating group due to strong – E, – I and – M effects.

–NO₂ is a powerful electron withdrawing group. Its presence on ring makes the ring less active

  (iso-butyl group)

Stability depends on number of hyperconjugative structures.

Conformers are form of stereoisomers in which isomers can be interconverted by rotations about single bonds. I and II are staggered and eclipsed conformers respectively.

Stability depends on number of hyperconjugative structure.

In the carbonium ion the carbon atom carrying the positive charge is sp² hybridized.

The blue colour is of  Fe₄ [Fe(CN)₆]₃