Lecture 6: Chemistry of Alkanes

Question 1

general formula of alkanes

Answer 1

CnH2n+2

Question 2

general formula of cycloalkanes

Answer 2

CnH2n

Question 3

what are homologous series?

Answer 3

same general formula
similar chemical properties

Question 4

types of carbons

Answer 4

primary, secondary, tertiary, quaternary

Question 5

types of hydrogens

Answer 5

primary, secondary, tertiary

Question 6

whats the difference between different types of carbons and hydrogens?

Answer 6

different bond strengths and reactivities

Question 7

nucleophiles description

Answer 7

1. high electron density
2. donates pair of electrons
3. Nu^-

Question 8

electrophile description

Answer 8

1. low electron density
2. accepts an electron pair
3. E^+

Question 9

description of alkanes

Answer 9

1. non-polar
2. unreactive to electrophiles and nucleophiles
3. alkanes react to free radicals

Question 10

description of free radicals

Answer 10

made by homolytic fission
have an unpaired electron
unstable
very reactive

Question 11

what is spin paired molecule?

Answer 11

all electrons are paired up
no extra charges

Question 12

what helps free radical reactions take place?

Answer 12

they require heat or light as an energy source

Question 13

initiation reaction formula

Answer 13

spin-paired molecule —> radical + radical

Question 14

propagation reaction formula

Answer 14

radical + spin-paired —> spin-paired molecule + radical

(2 reactions always- chain reactions)

Question 15

termination reaction formula

Answer 15

radical+ radical —> spin-paired molecule

Question 16

what factors facilitate homolytic fission?

Answer 16

1. atoms have a similar electronegativity (small electronegativity difference)
2. bond is weak

Question 17

when does monosubstitution happen?

Answer 17

excess of alkane

Question 18

when does multiple substitution happen?

Answer 18

excess of chlorine/bromine/iodine

Question 19

factors determining major products

Answer 19

1. C-H bond strength
2. stability of radical formed

Question 20

what is the dominant factor between probability and bond strength+stability of radical to determine major product?

Answer 20

bond strength+stability

Question 21

what is more selective: chlorination or bromination?

Answer 21

bromination

Question 22

why is it better to do bromination reactions?

Answer 22

1. it is highly selective so there’s less waste (major product only determined by chemical factors)
2. there’s only one major product; no wasteful side products
3. there’s no mixture of products which means there’s no trouble separating products