organic basics - functional groups

Question 1

functional group definition

Answer 1

small groups of atoms that dictate the reactivity of a molecule, often distinctive and often containing the elements O, N, S, P

Question 2

alkane definition + reactivity + uses

Answer 2

simplest class of organic molecules, essentially ‘no functional group’
very unreactive, undergo combustion and some radical reactions
can be used as fuels or solvents as relatively inert

Question 3

alkene definition + reactivity

Answer 3

characterised by C=C bond, trigonal planar so flat
much more reactive than alkanes, can undergo hydration, oxidation, reduction, polymerisation

Question 4

aromatic ring definition + reactivity + uses

Answer 4

rings stabilised by delocalised π system, trigonal planar so flat
reactivity is different to isolated alkenes (can be better or worse depending on substituents)
commonly used in drugs

Question 5

alkynes definition + reactivity + uses

Answer 5

characterised by C≡C bond, linear structure, do not often form cyclic structures in smaller rings
very reactive
used widely in drugs, uncommon in nature

Question 6

allenes definition

Answer 6

characterised by C=C=C group, twisted structure

Question 7

compare reactivities of dewar benzene vs regular benzene

Answer 7

benzene is much more stable as an aromatic ring, as dewar benzene is higher in energy it is also more reactive

Question 8

allyl group definition

Answer 8

a C=C double bond with an extra C attached:
C=C-C

Question 9

how are allyls made and what are its 2 ionic variants?

Answer 9

allyls can be made from haloalkenes where halogen X is not bonded to C=C group
ionic variants:
allyl cation C=C-C+
allyl anion C=C-C-

Question 10

give the rough structure for a primary aromatic amide functional group

Answer 10

Ar-NH2

Question 11

give the rough structure for a sulphonamide functional group

Answer 11

-SO2NH2

Question 12

give the rough structure for a hydrazine functional group

Answer 12

-NHNH2

Question 13

give the rough structure for a hydrazide functional group

Answer 13

-CONHNH2

Question 14

how do carbonyl groups react?

Answer 14

C=O bond consists of a strong σ bonds and a weaker π bond - overall = a strong bond
all chemical reactions via C=O involves π* orbital = LUMO, quite low in energy due to dipole of bond lowering energy of the orbital
3 main sites of reaction are:
δ- O with lewis basic lone pair, so can react with acts
δ+ electrophilic C susceptible to attack from nucleophiles
α acidic protons, allows carbonyls to act as a conjugate base = a nucleophile

Question 15

ketone definition + reactivity

Answer 15

characterised by R2C=O group
reacts well with nucleophiles

Question 16

aldehyde definition + reactivity

Answer 16

characterised by R-C(=O)-H group
reacts well with nucleophiles

Question 17

carboxylic acid definition + reactivity

Answer 17

characterised by COOH group
has many adjacent protons that are acidic

Question 18

acyl chloride definition + reactivity

Answer 18

characterised by R-C(=O)-Cl group
Cl = good LG, very good electrophile

Question 19

ester definition

Answer 19

characterised by R-C(=O)-OR group

Question 20

lactone definition

Answer 20

a cyclic ester - has different reactivity to aliphatic esters

Question 21

amide definition

Answer 21

characterised by R-C(=O)-NH- group

Question 22

lactam definition

Answer 22

cyclic amide - has different reactivity to aliphatic group

Question 23

acid anhydride definition + reactivity

Answer 23

R-C(=O)-O-C(=O)-R group
very good carbonyl electrophile, only a bit less reactive than acyl chloride

Question 24

imide definition + reactivity

Answer 24

N derivative of acid anhydride
R-C(=O)-NH-C(=O)-R group
reactivity between ester and ketone

Question 25

imine definition

Answer 25

N derivative of aldehyde/ketone H/R2C=N-...

Question 26

enol definition

Answer 26

ketones + aldehydes can convert into enols characterised by R=C(-OH)-R these lose their hydroxyl proton to form enolates, which are very stablised by -ve charge delocalised across molecule - tautomer of ketones/aldehydes

Question 27

enamine definition

Answer 27

imines can convert into enamines, N derivative of enol R=C(-NHR)-R

Question 28

give the carbonyl reactivity series

Answer 28

in order of increasing reactivity + decreasing delocalisation: carboxylic acid amide ester imide ketone aldehyde acid anhydride acyl chloride

Question 29

rationalise the place of acyl chlorides in the carbonyl reactivity series

Answer 29

Cl = very electronegative and so pulls a lot of electron density towards itself making the carbonyl C more electrophilic however Cl has 3 lone pairs in its 3p orbitals which don't overlap well with the π-system, making it ever more electron withdrawing, and so its activity increases

Question 30

rationalise the place of acid anhydrides in the carbonyl reactivity series

Answer 30

central O has 2 lone pairs and is very electronegative but electrons are shared between 2 π=systems, overall O pulls more to itself that it puts back via mesomeric inductive effect

Question 31

rationalise the place of esters in the carbonyl reactivity series

Answer 31

O atoms donate more electron density than they remove so the carbonyl C becomes even more electrophilic

Question 32

rationalise the place of amides in the carbonyl reactivity series

Answer 32

N is less electronegative than O and only has 1 lone pair which is less tightly held to N than O, so N pushes more electron density into electrophilic C increasing electrophilicity

Question 33

rationalise place of carboxylic acids in carbonyl reactivity series

Answer 33

carboxylic acids act as acids due to acidic OH group, remember nucleophiles are basic, this reaction pushes electron density into C=O carbon making it even less reactive - technically not in seiries at all

Question 34

can aldehydes + ketones undergo substitution?

Answer 34

no, they sit in the middle of carbonyl reactivity series defined by their alkyl groups, which aren't acidic, so poor leaving groups so cannot undergo substitution at C=O centre

Question 35

are aldehydes or ketones more reactive + why?

Answer 35

aldehydes are more reactive as there is less steric hinderance around C=O, only one alkyl group so there is better access to electrophilic carbon and therefore better/faster reactions - consider burgi-dunitz angle of attack

Question 36

are aliphatic carbonyls more or less reactiv e than aromatic carbonyls?

Answer 36

aliphatic carbonyls are more reactive they have hyperconjugation and inductive effects but aromatic π-system situtation is much more stablilising so aliphatic aldehydes/ketones>aromatic aldehydes/ketones

Question 37

tautomerisation definition

Answer 37

an intramolecular transfer of a proton from 1 atom to another in a molecule

Question 38

tautomer definition

Answer 38

isomers differing in only the position of H atoms and electrons

Question 39

acetal definition

Answer 39

R-C(-OR)2 group - the R groups on each O do not need to be the same

Question 40

hemi acetal definition

Answer 40

R-C(-OH)-OR group where one of the 'R' groups is a H, so juts a hydroxyl group

Question 41

hemi amenal definition

Answer 41

R-C(-OH)-NH3/R3 - a semi N derivative of a hemi acetal

Question 42

aldol definition

Answer 42

R-C(=O)-C-C(OH)R2 - a carbonyl bonded to a carbon bonded to tertiary alcohol