Block 4 - Functional Groups I

Question 1

types of halides

Answer 1

alkyl halides, vinyl halides (halogen to C in C=C), aryl halide

Question 2

types of -OH containing compounds

Answer 2

alcohols, enols (-OH to C in C=C), phenol (aromatic ring)

Question 3

classification of halides/alcohols exceptions

Answer 3

not used in aromatic rings or C=C ones as the C is not sp3 (but used in regular cyclic compounds - sp3 C)

Question 4

need for classification

Answer 4

same functional group containing compounds display similar reactivity but specifics of HOW they react can be influenced by presence of neighbouring atoms

Question 5

types of amines

Answer 5

alipathic (alkyl chain), aromatic (1+ bonds on N is to a ring)

Question 6

classification of amines

Answer 6

number of C-N bonds there are (chemistry usually takes place at N)
- still used in aromatic amines

Question 7

alcohol/amine solubility

Answer 7

soluble up to C5

Question 8

alkyl halide solubility

Answer 8

non-polar => good organic solvents

- unsustainable

Question 9

weak nucleophiles

Answer 9

neutral compounds containing O (O very electronegative so two lone pairs less available for reaction)

Question 10

weak nucleophile examples

Answer 10

water, alcohols, carboxylic acids

Question 11

moderate nucleophiles

Answer 11

conjugate base (low basicity)
- negatively charged => decent nucleophiles

Question 12

moderate nucleophile examples

Answer 12

halides, cyano anions, carboxylate anions

Question 13

strong nucleophiles

Answer 13

high basicity

1) O with formal negative charge
2) C with negative charge (carbon-centred nucleophiles)
3) charged AND uncharged nitrogen species

Question 14

O with formal negative charge

Answer 14

hydroxide, alkoxide (require very strong base to generate from alcohol)

Question 15

C with negative charge

Answer 15

alkynide (deprotonated terminal alkyne - require very strong base to generate)

Question 16

nucleophilic substitution

Answer 16

involves replacing one nucleophile with another

Question 17

Good leaving groups

Answer 17

halides (Cl- < Br- < I-)

- better leaving group => faster reaction

Question 18

poor leaving groups

Answer 18

H-, NH2-, HO-, RO-

Question 19

SN1 unimolecular mechanism

Answer 19

1) halogen leaves to form carbocation intermediate (min. E) and halide ion (RDS)
2) nucleophile comes in
- two distinct steps

Question 20

SN1 rate

Answer 20

rate = k[RX]

- independent of Nu (strength of Nu may affect course of reaction but not rate as it reacts after RDS)

Question 21

SN1 favours

Answer 21

3º > 2º&raquo_space; 1º

+ benzylic halides (resonant stabilised carbocations)

Question 22

SN1 stereochemistry

Answer 22

loss of stereochemistry - either enantiomer gives racemic mixture as long as product is chiral

Question 23

SN2 bimolecular mechanism

Answer 23

concerted, synchronous - transition state (max. E) where bond partially formed and partially made

Question 24

SN2 rate

Answer 24

rate = k[RX][Nu]

- Nu involved in RDS

Question 25

SN2 favours

Answer 25

1º > 2º >> 3º | unstable carbocations + less sterically hindered (crowded have raised energy of transition state and Ea)

Question 26

SN2 stereochemistry

Answer 26

inversion of configuration - non-racemic 2º alkyl halide results in non-racemic prod. of opposite chirality (simultaneous bond breaking/making so nucleophile must come in from other side)

Question 27

alcohols as Nu

Answer 27

alcohol (weak Nu) + strong base -> alkoxide (strong Nu) | - chemistry at O

Question 28

strong base

Answer 28

NaNH2

Question 29

alcohols as electrophile (E+)

Answer 29

alcohol (bad leaving group) + acid -> oxonium (good leaving group) - acidic conditions = limited nucleophiles as reagents as most are charged/basic - chemistry at C

Question 30

reagents and mechanisms for alcohol -> alkyl halide

Answer 30

tertiary: SN1 HCl primary: SN2 SOCl2 (HCl too slow)

Question 31

amine + alkyl halide

Answer 31

product also amine which can act as nucleophile for another reaction

Question 32

product of sub. of amines

Answer 32

mixture of 1º, 2º, 3º and quarternary ammonium salts

Question 33

elimination

Answer 33

break sigma, form pi | - no classification as not adding/subbing nucleophile/electrophile

Question 34

alkyl halide -> alkenes

Answer 34

in presence of strong base

Question 35

alkyl halide -> alkynes

Answer 35

in presence of strong base | - dihalide -> alkyne

Question 36

alcohol elimination

Answer 36

in presence of strong acid - alcohol -> alkene NO ALKYNES from diols as enol intermediate unstable (forms corresponding carbonyl compound => tautomerises)

Question 37

E1 unimolecular mechanism

Answer 37

1) leaving group leaves to form carbocation - extra step for alcohol -> oxonium 2) C-H bond breaks for C=C

Question 38

E1 rate

Answer 38

rate = k[RX]

Question 39

E1 favours

Answer 39

3º > 2º >>> 1º

Question 40

E2 mechanism

Answer 40

leaving group departure and pi bond formation occur at same time

Question 41

E2 rate

Answer 41

rate = k[RX][Nu]

Question 42

E2 favours

Answer 42

1º alcohols, more complex for alkyl halides - in reality no particular preference for 1º as steric hindrance not a problem (depends more on strength of Nu) so actually slightly prefers 3º more due to stability

Question 43

enantiomers

Answer 43

all stereocentres reversed

Question 44

diastereomers

Answer 44

only some stereocentres reversed

Question 45

mutorotation

Answer 45

spontaneous change in optical rotation observed when a pure anomer of a sugar is dissolved in water and equilibriates to an equilibrium mixture of anomers

Question 46

glycosidic bond/linkage

Answer 46

bond between anomeric carbon of one sugar and -OH group of another - links two sugars together

Question 47

wheland intermediates

Answer 47

resonance stabilised carbocation intermediates