1. Introduction to Org chem

Question 1

define homolytic fission

Answer 1

breaking of covalent bond such that one electron goes to each of the atoms, forming free radicals

Question 2

define heterolytic fission

Answer 2

breaking of covalent bond such that both electrons go to the SAME atom, forming +ve and -ve ions (cation being the carbocation)

Question 3

what kind of bond cleavage forms free radicals?

Answer 3

homolytic fission

Question 4

electrophiles are lewis acids or base?

Answer 4

acid

Question 5

characteristics of electrophiles [3]

Answer 5

1. are electron deficient
2. attracted to regions of -ve charge or electron rich regions
3. may possess an empty orbital to accept election pair

Question 6

characteristics of radicals

Answer 6

contains unpaired electron formed from the homolytic fission of a covalent bond

Question 7

does steric hindrance increase or decrease a moelcule’s reactivity? why?

Answer 7

decrease. prevents approach of an attacking reactant and either prevents reaction from taking place or lowers reactivity of a particular site within molecule

Question 8

what is the electronic effect?

Answer 8

can be either electron withdrawing or donating.
An atom or a group of atoms can increase/decrease electron density to a compound. can understand it as the momentary giving/receiving of electrons

Question 9

state the 2 broad groups of isomerism. differentiate the 2.

Answer 9

constitutional isomerism and stereoisomerism
constitutional: same molecular formula but diff structural formula
stereoisomerism: same molecular formula, same structural formula but diff spatial arrangement of functional groups

Question 10

prefix name for -NO2

Answer 10

nitro-

Question 11

prefix name for R-C=O [carbonyls]

Answer 11

oxo-

Question 12

prefix name for -NH2

Answer 12

amino-

Question 13

prefix name for -OH

Answer 13

hydroxy-

Question 14

prefix name for -CN

Answer 14

cyano-

Question 15

electrophilic addition occurs only in ___?

aka electrophiles added

Answer 15

alkenes

Question 16

addition reactions occurs when compound is saturated or unsaturated?

Answer 16

unsaturated aka double bonds aka C=C or C=O bonds

Question 17

nucleophilic addition occurs in what kinds of compounds? [2]

Answer 17

ketones and aldehydes

Question 18

define hydrolysis

Answer 18

a reaction which water is used to break a bond

Question 19

define condensation reaction

Answer 19

2 molecules react tgt to form a bigger molecule with elimination of small molecules eg. H2O, HCl

Question 20

oxidation occurs when ___ [4]

hint: what kinds of atoms are added/removed

Answer 20

1. oxygen from oxidising agent is added
2. H atom removed
3. loss of electron
4. increase in O.N

Question 21

state the 3 kinds of constitutional isomerism

Answer 21

1. chain isomerism
2. positional isomerism
3. functional group isomerism

Question 22

what kind of constitutional isomerism do these compounds show?

Answer 22

chain isomerism
- essentially the same molecular formula C4H10 but differs in straight chain vs branched chain

Question 23

what kind of constitutional isomerism do these compounds show?

Answer 23

positional isomers
- functional groups located at different part of the same carbon skeleton

Question 23

what kind of constitutional isomerism do these compounds show?

Answer 23

positional isomers
- functional groups located at different part of the same carbon skeleton

Question 24

what is functional group isomerism? [2]

Answer 24

criteria to fulfill 1. both compounds have SAME molecular formula 2. but have different functional groups

Question 25

cis isomer has 2 identical groups on same/opposite side of the double bond?

Answer 25

same side | **c**is-**s**ame

Question 26

for cis-trans isomers, cis isomers has higher/lower boiling point than their respective trans-isomer? explain

Answer 26

higher. cis isomers have higher polarity so additional pd-pd forces require more heat energy to overcome

Question 27

criteria for enantiomerism [3]

Answer 27

1. forms non-superimposable mirror image 2. contains chiral centres 3. does not have internal plane of symmetry

Question 28

a chiral carbon is ___-hybridised | type of hybridisation: sp/sp2/sp3 ?

Answer 28

sp3

Question 29

define racemic mixture

Answer 29

when theres is equal proportions of (+) and (-) enantiomers formed

Question 30

characteristics of meso compound [3]

Answer 30

1. **superimposable** mirror image even though they contain chiral centres 2. contains **internal plane of symmetry** [which causes point 1] 3. optically inactive

Question 31

name the type of hybridisations & describe [3]

Answer 31

1. sp hybridisation - 1 2s orbital combine with 1 2p orbital to form 2 identical sp orbitals - occurs when 2 σ bonds & 2 π bonds are formed 2. sp2 hybridisation - 1 2s orbital combine with 2 2p orbital to form 3 identical sp2 orbitals - occurs when 3 σ bonds & 1 π bond is formed 3. sp3 hybridisation - 1 2s orbital combine with 3 2p orbital to form 4 identical sp3 orbitals - occurs when 4 σ bonds are formed

Question 32

for IUPAC Naming, suffix is always the principal functional group. when there are more than 1 functional group, what is the order for precedence?

Answer 32

carboxylic acid / acyl halide / aldehyde / ketone > alcohol > amine > alkene

Question 33

characteristics of nucleophiles [3]

Answer 33

1. are electron rich 2. attracted to regions of +ve charge or electron deficient regions 3. usually molecules with at least 1 lone pair of electrons

Question 34

criteria for cis-trans isomers [2]

Answer 34

1. restricted rotation in certain parts of the molecule due to π bond 2. 2 different groups attached to the same atom of the π bond

Question 35

why is the smallest cycloalkene to show cis-trans isomerism is cyclooctene?

Answer 35

the min no. of carbons in cycloalkanes to display cis-trans isomerism is 8. a cycloalkene with less than 8C gives only a cis isomer as the existence of a trans isomer will give rise to severe ring strain & hence instability.

Question 36

what's the no. of possible cis-trans isomers present in a compound?

Answer 36

2^m , where m is the no. of double bonds that gives rise to cis-trans isomerism

Question 37

what's the no. of enantiomers present in a compound?

Answer 37

2^n, where n is the no. of chiral centres

Question 38

what's the no. of stereoisomers present in a compound which exhibits both cis-trans isomerism & enantiomers?

Answer 38

2^m+n, where m is the no. of double bonds exhibiting cis-trans isomerism & n is the no. of chiral centres exhibiting enantiomerism

Question 39

name all mechanisms for each functional group

Answer 39

1. alkanes - free radical sub 2. alkenes - electrophilic addition 3. arenes - electrophilic substitution 4. halogenoalkanes - nucleophilic sub 5. carbonyls - nucleophilic addition