a. 1. `SN^(-1), 3^(@)`
2. `CH_(3)CH_(2)CH_(3) + HBr, SN^(2), 1^(o+)` ha,ode. Nuclelphile is `H^(o+)` (hydride ion).
3. `1-CH_(2)CH_(2) CH_(3). SN^(2), 1^(@)` halide, `I^(@)` good nucleoophile and poor base.
4. `(CH_(3))_(2) C = CH_(2) .E2.3^(@)` halide and `CN^(ᶱ)` is a strong base, so eleimination is presominant over `SN^(-1)`.
5. `CH_(3)CHOHCH_(3). SN^(2)`. polar solvenet favours substitution.
6. `CH_(2) - CH = CH_(2). E2`, less polar solvent favours `E2`
7. `(CH_(3))_(3)C - OH, SN^(-1), H_(2)O` is not basic enough to remove a proton to give elimation reaction.
b. 1. `(i)gt(iii)gt(ii) (3^(@) gt 2^(@) gt 1^(@)` alkuyl halide) `SN^(-1)`.
2. `(ii) gt (iii) gt (i)` (`1^(@) gt 2^(@) gt 3^(@)` alkyl halide, `SN^(2)`)
3. `(i) gt (iii) gt (ii)`, Heavy ions, such as `Ag^(o+)` or `Pb^(*2+)` catayse `SN^(-1)`
Half of the molecules are inverted and rest half are retained. So theproduct is `(+-)`.
When the mucleiphile and leaving groups are same, product is alwyas racemic, although the reaction proceeds via `SN^(2)` mechanism.
d. 1. `(iv) gt (III0 gt (ii) gt (i)`, 2. `(i) gt (ii) gt (iii) gt (iv) gt (v)`
Alkyl group echances ionisation in the order `Megt Et i-Pr gtMN t-Bu` (Hyperconjugation) Nitoro group retards ionisation, due to `overline(e)` withdrawing effect of this group.
It is therefore clear that `overline(e)` withdrawing group will favor `SN^(-2)` mechanism for a compound with an `alpha-` halogen atom. Such groups aare `COOR, NO_(2), CN`, etc.e.g., both ethyl `-alpha-` bromonpropionate `(CH_(3) - CH(Br) - COOC_(2)H_(5))` and diethuylbromomalonate
`(C+_(2) H_(5) OOC - CH(Br) - COOC_(2)H_(5))` undergo hydroysis by `SN^(2)` mechanism.
On the other hand, `COO^(ᶱ)` ion has `+I` effect,m as due to its negative charge it ionises the `alpha-` halogen atom, Also `delta` charge on `alpha-C` atom opposes the approach of nucleophile.
e. 1. `(iii) gt (ii) gt (i)` (Group leability is `I^(-) gt Br gt Cl^(-)`)
2. `(vii) gt (v) gt (vi)` (Steric factor makes the reactivity `1^(@)gt 2^(@) gt 3^(@)`)
3. `(vii) gt (ix) gt (viii)`
(Viii) is `3^(@)` and the slowest),
(ix) suffers from `beta-` substitution.
f. i. Optical purity of bromide `= (30^(@))/(36^(@)) xx 100 = 83%`
Optical purity of alcohol `= (-6.0^(@))/(-10.3) xx 100 = 58%`
ii. Percent inversion `= (58%)/(83%) xx 100% = 70%`
Percent racemisation `= 100% - 70% = 30%`
iii. Inversin involves only backsildes and frontside attacks. The percentage of caksisde attack is the sum of th inversion. and one half the percetage of racemisation. The percentage of forntside attack is the remaining half of the percentage of racemission.
Percentage of backside attack `= 70% + (1)/(2) (30%)`
Perctage of frontside attack `= (1)/(2) (30%) = 15%`
g. 1. Cyvlopropyl chloride is less reactive than cyclopentyl chloride in each type of reaction becuase the `sp^(2)-C` (`120^(@)` bond angle) created in each `T.S`. increases the ring strain.
2. Vinyl hlaides are inert towards both `SN^(-1)` and `SN^(2)` reactions.
i. In `SN^(-1)` reactions they would have to ionise vinyl cations, which are very unstable because of their `sp` hybridiasation.
ii. The stronger `(C-X)` bond is difficult to break due to resonance stablisation. SO `SN^(2)` is not possible.
h. a. Acidic character: `HF gt H_(2) O gt NH_(3) gt CH_(4)`
Basic character : `F^(ᶱ) lt underset(ᶱ)(O)H lt underset(ᶱ)(N)H_(2) lt underset(ᶱ)(C) H_(3)`
Stronger the acid, weaker is its conjuagate base.
i. a. When teh nucleophilic centre is same. Nucleophilicity is same as basic character:
`H_(3) O^(o+) gt CH_(3) COOH gt CH_(3)OH gt H_(2)O`
Basically and mucleophilicity:
`H_(2)O lt CH_(3) COO^(ᶱ) lt CH_(3) O^(ᶱ) lt overset(ᶱ)(O)H`
j. b. Weaker the base or stronger the acid, better is the leaving group,
Acidic character: `C_(6) H_(5) SO_(3) H gt CH_(3) COOH gt C_(6) H_(5) OH gt CH_(3)OH`
k. b. Acidic and leaving group order:
`CF_(3) SO_(3) rarr MeSO_(3) rarr AcO rarr MeO-`.
