org chem?

Question 1

Why phenol CANNOT undergo NS?

Answer 1

1. p orbital of O atom overlaps side on with the pi e cloud of the adjacent benzene ring.
2. this allows lp of e on O atom is delocalised into the ring
3. leading to partial double bond character in C-O bond
4. the strengthened C-O bond requires more energy to break

Question 2

electronegativity in alkanes

Answer 2

C-H non-polar
=> lack of e rich and e deficient sites
=> unreactive towards polar reagents (thats why only got FRS)

Question 3

electronegativity in alkenes

Answer 3

C=C bond is e rich + non-polar
=> reactive towards E+
=> thats why can undergo EA

Question 4

electronegativity in RX

Answer 4

C-X bond is polar
=> C has partial positive charge
=> X has partial negative charge
=> partial positive C atom is E+ and susceptible to attack by Nu

Question 5

electronegativity in C=O

Answer 5

C=O bond is polar
=> C has partial positive charge
=> O has partial negative charge
=> partial positive C atom is E+ and susceptible to attack by Nu

Question 6

inductive effect in alkane

Answer 6

e-donating alkyl grps
=> stabilise carbon radical intermediate by
=> increasing e density of C atom w unpaired e

Question 7

inductive effect on alkenes

Answer 7

e-donating alkyl grps
=> stabilise carbocation intermediate by
=> dispersing + charge on C atom

Question 8

inductive effect on arenes

Answer 8

e-donating / e-withdrawing grp
=> increases/decreases e density on benzene ring
=> making ring in ___ stronger/weaker Nu than benzene

Question 9

inductive effect on RX (SN1)

Answer 9

e-donating alkyl grps
=> stabilise carbocation intermediate by
=> dispersing + charge on C atom

Question 10

inductive effect on ROH (talk abt R) vs H2O (acid)

Answer 10

e-donating alkyl grp
=> intensify - charge on O atom
=> RO- less stable than HO-

Question 11

inductive effect on carbonyl compounds (aldehyde more E+ than ketone)

Answer 11

1 less e-donating alkyl grp which makes
=> carbonyl carbon in aldehyde more E+

Question 12

inductive effect on CH2ClCOOH has smaller pKa than CH3COOH

Answer 12

e-withdrawing Cl atom
=> stabilises carboxylate anion by
=> dispersing - charge on O atom
=> CH2ClCOO- more stable than CH3COO-

Question 13

Ch3NH2 is stronger base than NH3

Answer 13

e-donating methyl grp
=> increases e density of N atom
=> making lp of e on N atom
=> more available for donation (dative bonding w proton)

Question 14

(ithink fyi)
define delocalisation

Answer 14

spreading of pi e over the whole system of atoms

Question 15

(i think fyi)
define inductive effect

Answer 15

effect of e donation or withdrawal felt by polarisation of the sigma bonds of the molecule

Question 16

define electronegativity

Answer 16

ability of an atom to attract the shared pair of e towards itself in a covalent bond

Question 17

delocalisation in benzene

Answer 17

all C atoms sp2 hybridised
=>unhybridised p oritals of C atoms are perpendicular to ring and
=> overlap side-on to
=> form a delocalised pi e cloud

Question 18

delocalisation in benzyl cation

Answer 18

+ charged C is sp2 hybridised
=> and has empty p orbital, which
=> overlaps side-on w pi e cloud of adjacent benzene ring
=> this allows pi e of benzene ring to be delocalised over + charged C
=> dispersing + charge

Question 19

(i think fyi)
define resonance effect

Answer 19

the effect of withdrawing or releasing e by a substituent in a molecule as a result of contact between a lp of e and pi bond, or interaction of 2 pi bonds separated by one single bond (<- conjugated pi bonds)

Question 20

define steric effeect

Answer 20

repulsion of e clouds of atoms dye to proximity(closeness) of arrangement in space

Question 21

what to do when there is a combi of effects?

Answer 21

1. cry
2. deep breaths
3. from data booklet, compare bond energy or compare activating and deactiviating grps to find out which effect is more dominant

Question 22

why mp of substitiuent (a carbonyl grp) in 2nd positin smaller than that at the 4th position in phenol?

Answer 22

• Both got simple molecualr structure
  2nd position: can form intramolecular H bonding due to close proximity of -OH in benzene ring and O atom of carbonyl grp. so less energy need to overcome less extensive intermolecular H bonding between molecules of A
• draw the intramolecular bonding, must include ||||:O(partial negative), H(partial positive)