Reasoning Flashcards
Benzyl chloride is highly reactive towards the SN1
reaction.
Due to the stability of benzyl carbocation due to
resonance
2-bromobutane is optically active but 1-
bromobutane is optically inactive
Because 2-Bromobutane has a chiral centre so mirror
image are nonsuperimposable
Electrophilic substitution reactions in haloarenes
occur slowly
Due to – I effect of halogen predominant over +R
effect
Which would undergo SN1 reaction faster
because 3o carbocation is more stable than
1o carbocation
Why haloarenes are less reactive than haloalkanes
towards nucleophilic substitution reactions
In haloarenes C—X bond acquires a partial double
bond character due to resonance
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
(i) iodine is a better leaving group because of its larger
size.
(ii) three bulky methyl group hinder the
approaching nucleophile
Which reacts faster in an SN1 reaction?
Compound (I) reacts faster in SN1 reaction as it is a 2°
alkyl halide
A solution of KOH hydrolyses CH3CH(Cl)CH2CH3 and
CH3CH2CH2CH2Cl. Which one of these is more easily hydrolysed and why?
CH3CH2ClCHCH3 more easily hydrolysed as it forms 2 secondary
carbocation which is more stable than 1 primary carbocation
State one use each of DDT and iodoform
DDT: It is used as insecticide Iodoform: Iodoform is
used as an antiseptic.
What is known as a racemic mixture? Give an
example.
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
Although chlorine is an electron withdrawing
group, yet it is ortho-, para-directing in
electrophilic aromatic substitution reactions.
Explain why it is so?
Through resonance effect, chlorine tends to stabilize
the carbocation and the effect is onlyapplicable at
ortho and para-positions
Grignard’s reagents should be prepared under anhydrous conditions, why?
This is because Grignard reagent forms alkanes by
reacting with moisture.
the dipole moment of Chlorobenzene is lower than that of Cyclohexyl chloride
due to resonance Chlorobenzene shorter
C-Cl
bond(sp2)than cyclohexyl chloride C—Cl bond(sp3)
Chloroform is stored in closed dark brown bottles
chloroform is slowly oxidised by air in the presence of
light to form poisonous gas phosgene.COCl2
p-nitro phenol is more acidic than p-methyl phenol
Due to –I/–R effect of –NO2 group & +I /+R effect of CH3
p-nitrophenol is more acidic than o-nitrophenol OR
O-nitrophenol is steam volatile ,not p-nitrophenol
p-nitro phenol has intermolecular H-bond while o-nitro
phenol has intramolecular H-bond.
Phenol is more acidic than ethanol.
phenoxide ion stabilised by resonance
Boiling point of ethanol is higher in comparison to
methoxymethane.
Because of hydrogen bonding in ethanol
The C – O – H bond angle in alcohols is slightly less
than the tetrahedral angle (109o28’)
Due to lone pair- lone pair repulsion on oxygen
Although phenoxide ion has more number of
resonating structures than carboxylate ion,
carboxylic acid is a stronger acid than phenol.
carboxylate ion stabilized through equivalent resonance
whereas phenoxide ion through non equivalent
resonance
Increasing order reactivity towards nucleophilic
addition OR (reactivity towards HCN)
C6H5CHO < CH3CHO <HCHO
Butanone < Propanone < Propanal < Ethanal
Methyl tert-butyl ketone < Acetone < Acetaldehyde
Acidic Character =(1/ pKa)
(CH3)2CHCOOH < CH3CH(Br) CH2COOH <
CH3CH2CH(Br)COOH
CH3COOH < Cl-CH2-COOH < F-CH2-COOH
4-Methoxy benzoic acid <Benzoic acid < 4-Nitrobenzoic
acid < 3, 4-Dinitrobenzoic acid.
Aldehydes are more reactive than ketones towards
nucleophilic addition
due to steric hinderence of 2-alkyl group in ketone
and more +I effect of 2-alkyl group in ketone
Cyclohexanone forms cyanohydrin in good yield but 2, 4, 6-trimethylcyclohexanone does not.
due to steric hindrance in 2, 4, 6-trimethyl
Carboxylic acids are higher BP than alcohols
due to more intermolecular hydrogen bonding
increasing order of basic strength , aqueous solutions
C6H5-NH2 < CH3-CH2-NH2 < (C2H5)3N <
C2H5-NH- C2H5NH3 < (CH3)3N <
CH3—NH2 < (CH3)2NH
increasing order of basic strength , gas phase
C6H5-NH2 < CH3-CH2-NH2 < C2H5-NH- C2H5< (C2H5)3N
In increasing order of solubility in water
(CH3)3N< CH3NHCH3 < CH3NH2
p-methylaniline is more basic than p-nitroaniline
―CH3 group +I – effect ,–NO2 group shows –I Effect
Acetylation of – NH2 group is done in aniline before preparing its ortho and para compounds
To reduce activating effect of –NH2 group
pKb for aniline is more than that for methylamine
In aniline due to resonance
Aniline does not undergo Friedel-Crafts reaction
Aniline Lewis base, reacts lewis acid AlCl3 to form salt.
Why do amines behave as nucleophiles?
Due to the presence of a lone pair
Aniline, p-nitroaniline and p-toluidine
p-Toluidine > Aniline > tr-nitroaniline
Aromatic primary amines cannot be prepared by
Gabriel phthalimide synthesis.
aryl halides do not undergo nuleophilic substitution
easily due to presence of partial double character
Although amino group is o– and p– directing in
electrophilic substitution reaction aniline on nitration
gives a substantial amount of m-nitroaniline.
In presence of conc HNO3 aniline gets protonated to
form the anilinium ion which is meta directing
