Organic Chemistry Flashcards
1
Q
Nucleophile
A
an electronegative functional group which has an electron pair that can be used to form a covalent bond
2
Q
Electrophile
A
an electron deficient functional group which accepts an electron pair to form a covalent bond
must have an empty orbital
3
Q
Aromaticity and Hunkel’s Rule
A
to be aromatic a compound must be planar and cyclic and have 4n+2 delocalised pi electrons, where n is an integer
4
Q
Hybridization
A
the mixing of atomic orbitals to make molecular orbitals
5
Q
sp3 hybridization
A
4 identical hybrid orbitals
tetrahedral
can have lone pair not involved in bonding available to hydrogen bond
6
Q
sp2 hybridization
A
3 identical hybrid orbitals
trigonal planar
p orbital not involved in bonding is at right angles to the plane and can for m a double bond
partial double bonds and resonance require this
7
Q
Tautomers
A
structural isomers differing in position of a hydrogen and a double bond
eg. keto to enol or imine to enamine
8
Q
Hydroxyl Group
A
- sp3 hybridisation
- 2 lone pairs
- electronegative
- H bonding
9
Q
Ether
A
- sp3 hybridization
- lone pairs but poor nucleophile
- unreactive
10
Q
Carboxylic Acid
A
- sp2 hybridisation of oxygen promotes delocalisation of lone pair
- forms carboxylate ion which acts as a base
11
Q
Ester
A
- sp3 hybridization of oxygen promotes delocalisation of lone pair
- reduces electrophilicity of carbonyl carbon and the nucleophilicity of the alpha carbon
- less reactive than carbonyl compounds
- less acidic because the ester O pushes its electrons into the system, competing with the carbonyl electrons
- partial double bond character and planar
12
Q
Carbonyl compounds (ketons/aldehydes)
A
- sp2 hybridization of oxygen promotes delocalisation of lone pair
- reactive electrophilic carbon
- acidic alpha carbon that acts as a nucleophile when deprotonated
13
Q
Enolate ion
A
- H removal from alpha carbon by a base from a carbonyl compound
- stabilised by delocalisation of charge over the system
- removal changes hybridisation to sp2 so that pi orbital overlap can occur to form a double bond
14
Q
Aldehydes
A
More reactive than ketones
- less steric hindrance as it lacks the R group
- inductive effect in which the alpha carbon shares some of its electron cloud with the carbonyl carbon, partially quenching the partial positive charge
15
Q
Amine
A
- sp3 hybridization
- one lone pair
- electronegative
- can be a base and a nucleophile only if deprotonated
- when protonated can donate a proton (acid)
16
Q
Amide
A
- sp3 hybridization of N promotes delocalisation of lone pair and reduces electrophilicity of carbonyl carbon, ie. reactivity reduced
- N is not basic or a nucleophile
- planar molecule
17
Q
Imine
A
- similar to carbonyl compounds
- N protonated at physiological pH so it is strongly polarised
- carbon highly electrophilic
18
Q
Schiff Base
A
- protonation of imine causes N to pull more electrons towards it because of its positive charge
- p orbital sharing to form double bond between N and C
19
Q
Thiol
A
- sulfur equivalent of hydroxyl
- more nucleophilic because its lone pairs are in level 3 and highly polarisable
- orbitals are too big for effective overlap with hydrogen so no hydrogen bonding
- not basic
- good leaving group
20
Q
Thioester
A
- sp3 hybridization as it couldn’t effectively overlap with 2p orbitals if sp2 hybridized
- no electron sharing with carbonyl
- similar reactivity to aldehydes
- no resonance
- alpha carbon is nucleophilic as S doesn’t interfere with enolate anion formation
- good leaving group as it is highly polarisable
21
Q
Nucleophilic Substitution (Sn1)
A
- two step mechanism
- nucleophilic attack from either side of the plane to form racemic mixture
- carbocation intermediate formed as X removes electrons
22
Q
Nucleophilic Substitution (Sn2)
A
- one step mechanism (concerted)
- forms transition state where both groups are attached via stretched p orbitals
- TS is sp2-like in the same plane as its substituents
- inversion of stereochemistry
23
Q
Elimination
A
- loss of a leaving group from a tetrahedral carbon together with a hydrogen from the adjacent carbon to form a C-C double bond
- need a base
- base pulls off hydrogen and leaving group leaves
- pi bond formed from p orbital overlap
- p orbitals form as groups leave
- change to sp2 hybridization in both carbons
24
Q
E2
A
- single step mechanism
- B attacks hydrogen
- electron flow back into C-C bond
- X pulls off electrons and leaves
- formation of sp2 like TS
25
Q
E1
A
- two step mechanism
- X leaves first and pulls off electrons
- carbocation intermediate with empty p orbital forms
- base attacks hydrogen and electrons flow into C-C bond
26
Q
Electrophilic Addition to C-C double bond
A
- pi cloud of the double bond acts as the nucleophile
- protons are electrophiles
- addition of a proton (from water) to the double bond gives carbocation intermediate that reacts with nucleophile (water) to give product
27
Q
Nucleophilic Addition
A
- carbonyl compounds without a leaving group
- nucleophilic attack at electrophilic carbonyl carbon (sp2 hybridized)
- as the bond forms between the carbonyl carbon and the nucleophile, the carbon and oxygen of the carbonyl group begin to change their hybridisation to sp3
- this provides the orbitals needed for bonding to the nucleophile and for the pi electrons to finish as a lone pair on the oxygen
- base pulls hydrogen off hydroxyl group
- attack on carbon and flow of electrons onto oxygen
- tetrahedral intermediate that is protonated to give the product
- protonation via attack on acid and breakage of acid hydrogen bond
28
Q
Imine formation
A
- nucleophilic addition
- addition of amine to aldehyde (or ketone) followed by loss of oxygen as water
29
Q
Hemiacetal Formation
A
- alcohol and aldehyde
- nucleophilic addition mechanism
- this then reacts with a second alcohol to form an acetal via a glycosidic linkage
- see notes for mechanism*
30
Q
Schiff Base (Imine) Formation
A
- amine + aldehyde
eg. lysine side chain and PLP - nucleophilic attack of N of amine on the carbonyl carbon
- electron flow back onto oxygen
- NH electron flow into N-C bond to make it a double bond and hydroxyl is protonated and leaves as water (is pushed off)
- unstable tetrehedral intermediate
31
Q
Nucleophilic Substitution
A
- carbonyl compounds with leaving groups
- mechanism the same as addition up to the formation of the tetrahedral intermediate
- base deprotonates water and nucleophilic attack on carbonyl carbon
- electrons flow back onto oxygen
- oxonium ion intermediate
- because there is a leaving group, electrons can flow back to reform the carbonyl pi cloud and the leaving group departs
- sp2 collapsed product
32
Q
Aldol Reactions
A
- nucleophilic attack of an enolate anion on a second carbonyl
- alpha carbon of second carbonyl is the nucleophile
33
Q
Aldol Addition
A
- electrophile doesn’t have a leaving group
- carbanion attack on carbonyl carbon
- electrons flow onto oxygen, which is protonated by an acid
- product: B hydroxy carbonyl
34
Q
Aldo Substitution
A
- electrophile has leaving group
- carbanion attack on carbonyl carbon
- electron flow onto oxygen
- formation of negative oxygen intermediate
- electrons flow back into C-O bond and leaving group leaves
- product: B keto carbonyl compound
