Organic chemistry - 3

Question 1

what does energy from photons promote?

Answer 1

promotes electrons from bonding/non-bonding to higher energy anti-bonding

Question 2

if there are only σ bonds what colour will the molecule be?

Answer 2

colourless

Question 3

what does HOMO mean?

Answer 3

highest occupied molecular orbital

Question 4

what does LUMO mean?

Answer 4

lowest unoccupied molecular orbital

Question 5

order the orbitals in order of decreasing energy (highest energy at top)

Answer 5

• π* anti-bonding
• σ* anti-bonding
• non-bonding
• π bonding
• σ bonding

Question 6

what is a conjugated system?

Answer 6

long carbon chain with alternating double and single bonds (σ and π)

Question 7

what will a large amount of conjugation result in?

Answer 7

coloured molecule

Question 8

what will happen to the wavelength if there is a greater number of atoms spanned by delocalised electrons?

Answer 8

smaller energy gap between HOMO and LUMO, longer wavelength absorbed

Question 9

what is a chromophore?

Answer 9

group of atoms within a molecule that is responsible for its colour

Question 10

if a molecule has 5 C=C what colour will it be?

Answer 10

yellow

Question 11

if a molecule has 11 C=C what colour will it be?

Answer 11

orange

Question 12

how is colour generated in an organic molecule?

Answer 12

• electrons absorb energy
• move from HOMO to LUMO
• colour complementary to that absorbed

Question 13

name three reactions to make alcohols

Answer 13

• hydration of alkenes
• nucleophilic substitution of haloalkane
• reduction of carbonyl compounds

Question 14

alkene + water -> ?

Answer 14

alcohol

Question 15

nucleophilic substitution: ? + ? -> alcohol

Answer 15

haloalkane + alkali -> alcohol

Question 16

what is the catalyst used in the reduction of carbonyl compounds to form an alcohol?

Answer 16

LiAlH4

Question 17

what can show the changing of a functional group?

Answer 17

infrared spectroscopy - parts of molecules vibrate

Question 18

what are optical isomers?

Answer 18

type of stereoisomers

- molecule contains tetrahedral carbon atom with four different groups attached to it

Question 19

what are enantiomers?

Answer 19

optically active stereoisomers that deflect the path of a beam of plane polarised light

Question 20

are enantiomers superimposable or non-superimposable?

Answer 20

non-superimposable

Question 21

what is a chiral centre?

Answer 21

four different groups attached to carbon

Question 22

what is a racemic mixture?

Answer 22

optically inactive, 50:50 mixture of two enantiomers

Question 23

why do alcohols have higher boiling points compared to other organic compounds?

Answer 23

polar OH group allows hydrogen bonding

Question 24

what happens to the solubility in water as chain increases?

Answer 24

decreases

Question 25

alcohol + carboxylic acid ?

Answer 25

alcohol + carboxylic acid ester +water

Question 26

alcohol + ? -> ester + salt

Answer 26

alcohol + acid chloride -> ester + salt

Question 27

produce an alkene from an alcohol

Answer 27

alcohol + catalyst -> alkene + water

Question 28

what catalysts can be used in the formation of an alkene through a dehydration reaction of alcohol?

Answer 28

• aluminium oxide
• c. sulphuric acid
• c. phosphoric acid

Question 29

what is the general structure of an ether?

Answer 29

R-O-R’

Question 30

why do ethers have lower b.p than isomeric alcohols?

Answer 30

hydrogen bonding doesn’t occur between molecules

Question 31

what are some properties of ethers?

Answer 31

• volatile
• highly flammable
• good solvents
• soluble in water (if small)

Question 32

equation to make ether

Answer 32

alkoxide + haloalkane -> ether

Question 33

what type of reaction is making an ether?

Answer 33

nucleophilic substitution reaction

Question 34

what is the purpose of nmr spectroscopy?

Answer 34

provides information about how many different chemical environments of protons there are in a molecule

Question 35

what is the area under the peak in NMR spectroscopy proportional to?

Answer 35

proportional to the number of protons in each environment

Question 36

what is the splitting of peaks caused by?

Answer 36

caused by neighbouring carbon’s hydrogen atoms

Question 37

how can the number of peaks in cluster be determined?

Answer 37

n + 1 (n = number of H on next door carbon)