Block 4 - Functional Groups I Flashcards
types of halides
alkyl halides, vinyl halides (halogen to C in C=C), aryl halide
types of -OH containing compounds
alcohols, enols (-OH to C in C=C), phenol (aromatic ring)
classification of halides/alcohols exceptions
not used in aromatic rings or C=C ones as the C is not sp3 (but used in regular cyclic compounds - sp3 C)
need for classification
same functional group containing compounds display similar reactivity but specifics of HOW they react can be influenced by presence of neighbouring atoms
types of amines
alipathic (alkyl chain), aromatic (1+ bonds on N is to a ring)
classification of amines
number of C-N bonds there are (chemistry usually takes place at N)
- still used in aromatic amines
alcohol/amine solubility
soluble up to C5
alkyl halide solubility
non-polar => good organic solvents
- unsustainable
weak nucleophiles
neutral compounds containing O (O very electronegative so two lone pairs less available for reaction)
weak nucleophile examples
water, alcohols, carboxylic acids
moderate nucleophiles
conjugate base (low basicity) - negatively charged => decent nucleophiles
moderate nucleophile examples
halides, cyano anions, carboxylate anions
strong nucleophiles
high basicity
1) O with formal negative charge
2) C with negative charge (carbon-centred nucleophiles)
3) charged AND uncharged nitrogen species
O with formal negative charge
hydroxide, alkoxide (require very strong base to generate from alcohol)
C with negative charge
alkynide (deprotonated terminal alkyne - require very strong base to generate)
nucleophilic substitution
involves replacing one nucleophile with another
Good leaving groups
halides (Cl- < Br- < I-)
- better leaving group => faster reaction
poor leaving groups
H-, NH2-, HO-, RO-
SN1 unimolecular mechanism
1) halogen leaves to form carbocation intermediate (min. E) and halide ion (RDS)
2) nucleophile comes in
- two distinct steps
SN1 rate
rate = k[RX]
- independent of Nu (strength of Nu may affect course of reaction but not rate as it reacts after RDS)
SN1 favours
3º > 2º»_space; 1º
+ benzylic halides (resonant stabilised carbocations)
SN1 stereochemistry
loss of stereochemistry - either enantiomer gives racemic mixture as long as product is chiral
SN2 bimolecular mechanism
concerted, synchronous - transition state (max. E) where bond partially formed and partially made
SN2 rate
rate = k[RX][Nu]
- Nu involved in RDS
SN2 favours
1º > 2º»_space; 3º
unstable carbocations + less sterically hindered (crowded have raised energy of transition state and Ea)
SN2 stereochemistry
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)
alcohols as Nu
alcohol (weak Nu) + strong base -> alkoxide (strong Nu)
- chemistry at O
strong base
NaNH2
alcohols as electrophile (E+)
alcohol (bad leaving group) + acid -> oxonium (good leaving group)
- acidic conditions = limited nucleophiles as reagents as most are charged/basic
- chemistry at C
reagents and mechanisms for alcohol -> alkyl halide
tertiary: SN1 HCl
primary: SN2 SOCl2 (HCl too slow)
amine + alkyl halide
product also amine which can act as nucleophile for another reaction
product of sub. of amines
mixture of 1º, 2º, 3º and quarternary ammonium salts
elimination
break sigma, form pi
- no classification as not adding/subbing nucleophile/electrophile
alkyl halide -> alkenes
in presence of strong base
alkyl halide -> alkynes
in presence of strong base
- dihalide -> alkyne
alcohol elimination
in presence of strong acid
- alcohol -> alkene
NO ALKYNES from diols as enol intermediate unstable (forms corresponding carbonyl compound => tautomerises)
E1 unimolecular mechanism
1) leaving group leaves to form carbocation
- extra step for alcohol -> oxonium
2) C-H bond breaks for C=C
E1 rate
rate = k[RX]
E1 favours
3º > 2º»_space;> 1º
E2 mechanism
leaving group departure and pi bond formation occur at same time
E2 rate
rate = k[RX][Nu]
E2 favours
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
enantiomers
all stereocentres reversed
diastereomers
only some stereocentres reversed
mutorotation
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
glycosidic bond/linkage
bond between anomeric carbon of one sugar and -OH group of another
- links two sugars together
wheland intermediates
resonance stabilised carbocation intermediates
