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Chemistry 101 > Reasoning > Flashcards

Reasoning Flashcards

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1
Q

Benzyl chloride is highly reactive towards the SN1
reaction.

A

Due to the stability of benzyl carbocation due to
resonance

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2
Q

2-bromobutane is optically active but 1-
bromobutane is optically inactive

A

Because 2-Bromobutane has a chiral centre so mirror
image are nonsuperimposable

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3
Q

Electrophilic substitution reactions in haloarenes
occur slowly

A

Due to – I effect of halogen predominant over +R
effect

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4
Q

Which would undergo SN1 reaction faster

A

because 3o carbocation is more stable than
1o carbocation

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5
Q

Why haloarenes are less reactive than haloalkanes
towards nucleophilic substitution reactions

A

In haloarenes C—X bond acquires a partial double
bond character due to resonance

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6
Q

Which compound in each of the following pairs will
react faster in SN2 reaction? Why?
(i) CH3Br or CH3I
(ii) (CH3)3C-Cl or CH3-Cl

A

(i) iodine is a better leaving group because of its larger
size.

(ii) three bulky methyl group hinder the
approaching nucleophile

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7
Q

Which reacts faster in an SN1 reaction?

A

Compound (I) reacts faster in SN1 reaction as it is a 2°
alkyl halide

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8
Q

A solution of KOH hydrolyses CH3CH(Cl)CH2CH3 and
CH3CH2CH2CH2Cl. Which one of these is more easily hydrolysed and why?

A

CH3CH2ClCHCH3 more easily hydrolysed as it forms 2 secondary
carbocation which is more stable than 1 primary carbocation

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9
Q

State one use each of DDT and iodoform

A

DDT: It is used as insecticide Iodoform: Iodoform is
used as an antiseptic.

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10
Q

What is known as a racemic mixture? Give an
example.

A

An equi-molar mixture of d- and l- isomers(50:50 d+l)
For example, butan-2-ol. A racemic mixture is optically
inactive due to external compensation

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11
Q

Although chlorine is an electron withdrawing
group, yet it is ortho-, para-directing in
electrophilic aromatic substitution reactions.
Explain why it is so?

A

Through resonance effect, chlorine tends to stabilize
the carbocation and the effect is onlyapplicable at
ortho and para-positions

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12
Q

Grignard’s reagents should be prepared under anhydrous conditions, why?

A

This is because Grignard reagent forms alkanes by
reacting with moisture.

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13
Q

the dipole moment of Chlorobenzene is lower than that of Cyclohexyl chloride

A

due to resonance Chlorobenzene shorter
C-Cl
bond(sp2)than cyclohexyl chloride C—Cl bond(sp3)

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14
Q

Chloroform is stored in closed dark brown bottles

A

chloroform is slowly oxidised by air in the presence of
light to form poisonous gas phosgene.COCl2

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15
Q

p-nitro phenol is more acidic than p-methyl phenol

A

Due to –I/–R effect of –NO2 group & +I /+R effect of CH3

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16
Q

p-nitrophenol is more acidic than o-nitrophenol OR
O-nitrophenol is steam volatile ,not p-nitrophenol

A

p-nitro phenol has intermolecular H-bond while o-nitro
phenol has intramolecular H-bond.

17
Q

Phenol is more acidic than ethanol.

A

phenoxide ion stabilised by resonance

18
Q

Boiling point of ethanol is higher in comparison to
methoxymethane.

A

Because of hydrogen bonding in ethanol

19
Q

The C – O – H bond angle in alcohols is slightly less
than the tetrahedral angle (109o28’)

A

Due to lone pair- lone pair repulsion on oxygen

20
Q

Although phenoxide ion has more number of
resonating structures than carboxylate ion,
carboxylic acid is a stronger acid than phenol.

A

carboxylate ion stabilized through equivalent resonance
whereas phenoxide ion through non equivalent
resonance

21
Q

Increasing order reactivity towards nucleophilic
addition OR (reactivity towards HCN)

C6H5CHO < CH3CHO <HCHO

A

Butanone < Propanone < Propanal < Ethanal

Methyl tert-butyl ketone < Acetone < Acetaldehyde

22
Q

Acidic Character =(1/ pKa)
(CH3)2CHCOOH < CH3CH(Br) CH2COOH <
CH3CH2CH(Br)COOH

A

CH3COOH < Cl-CH2-COOH < F-CH2-COOH
4-Methoxy benzoic acid <Benzoic acid < 4-Nitrobenzoic
acid < 3, 4-Dinitrobenzoic acid.

23
Q

Aldehydes are more reactive than ketones towards
nucleophilic addition

A

due to steric hinderence of 2-alkyl group in ketone
and more +I effect of 2-alkyl group in ketone

24
Q

Cyclohexanone forms cyanohydrin in good yield but 2, 4, 6-trimethylcyclohexanone does not.

A

due to steric hindrance in 2, 4, 6-trimethyl

25
Q

Carboxylic acids are higher BP than alcohols

A

due to more intermolecular hydrogen bonding

26
Q

increasing order of basic strength , aqueous solutions

A

C6H5-NH2 < CH3-CH2-NH2 < (C2H5)3N <
C2H5-NH- C2H5NH3 < (CH3)3N <
CH3—NH2 < (CH3)2NH

27
Q

increasing order of basic strength , gas phase

A

C6H5-NH2 < CH3-CH2-NH2 < C2H5-NH- C2H5< (C2H5)3N

28
Q

In increasing order of solubility in water

A

(CH3)3N< CH3NHCH3 < CH3NH2

29
Q

p-methylaniline is more basic than p-nitroaniline

A

―CH3 group +I – effect ,–NO2 group shows –I Effect

30
Q

Acetylation of – NH2 group is done in aniline before preparing its ortho and para compounds

A

To reduce activating effect of –NH2 group

31
Q

pKb for aniline is more than that for methylamine

A

In aniline due to resonance

32
Q

Aniline does not undergo Friedel-Crafts reaction

A

Aniline Lewis base, reacts lewis acid AlCl3 to form salt.

33
Q

Why do amines behave as nucleophiles?

A

Due to the presence of a lone pair

34
Q

Aniline, p-nitroaniline and p-toluidine

A

p-Toluidine > Aniline > tr-nitroaniline

35
Q

Aromatic primary amines cannot be prepared by
Gabriel phthalimide synthesis.

A

aryl halides do not undergo nuleophilic substitution
easily due to presence of partial double character

36
Q

Although amino group is o– and p– directing in
electrophilic substitution reaction aniline on nitration
gives a substantial amount of m-nitroaniline.

A

In presence of conc HNO3 aniline gets protonated to
form the anilinium ion which is meta directing

37
Q
A

Chemistry 101 (1 decks)

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