U2 KA2- Organic synthesis

Question 1

Double headed curly arrows

Answer 1

Used to indicate the movement of electrom pairs in a reaction
* tail is where the electrons orginate from

Question 2

Single headed curly arrows

Answer 2

Indicates the movement of a single electron

Question 3

Heterolytic bond fission

Answer 3

• occurs when a covaent bonod between 2 chemical species is broken in an unequal manner
• bond pair of electrons being retained by one of the chemical species

Question 4

Homolytic bond fission

Answer 4

• occurs when the bond is non polar or very slightly polar
• one electrom from bond goes to one atom while the other electron goes to the other atoms

Question 5

Production of free radicals

Answer 5

1. chain initiation- UV light makes Br into free radicals
2. chain propogation- one radical enters reaction and one is formed
3. chain termination- remove free radicals from reaction ithout replacing new ones

Question 6

How are ions formed?

Answer 6

by heterolytic fission
(favoured when the bond is polar)

Question 7

Electrophile

Answer 7

positively charged ions
can accept electron pair

Question 8

Nucleophiles

Answer 8

Negatively charged ions
at least 1 lone pair of electrons
electron dontating

Question 9

Haloalkanes

Also known as halogenoalkanes

Answer 9

one or more H replaced with a halogen atom

Question 10

What is the difference between primary, secondary and tirtiary monohaloalkane?

Answer 10

Primary- one alkyl group attached to the carbon atom directly atached to the halogen atom
Secondary- 2
Tirtiary- 3

Question 11

Why are haloalkanes susceptible to nucleophilic attack?

Answer 11

the presence of the slight positive charge on the carbon atom (polar nature)

Question 12

Nucleophilic substitutions

Answer 12

Reactions of monoalkanes with alkalis to produce alcohol
* Potassium hydroxide (KOH) or Sodium hydroxide (NaOH) is used
* reaction with alcoholic potassium alkoxide produces ethers
* reaction with ethanolic potassiym cyanide or sodium cyanide (KCN/NaCN in ethanol) produces nitriles increases chain length and nitrile can be converted into carboxylic acid through acid hydrolysis

Question 13

Sn1

Answer 13

first order nucleophilic substitution

Question 14

Sn2

Answer 14

Second order nucleophilic substitution

Question 15

What is formed in the Sn1 reaction?

Answer 15

A carbocation intermediate (tirtiary is most stable)
positively charged intermediate

Question 16

What is formed in a Sn2 reaction?

Answer 16

negatively charged intermediate is formed

Question 17

How are elimination reactions achieved?

Answer 17

When monohaloalkanes undergo elimination reactions to form alkenes
* heating monohaloalkane under reflux with ethanolic potassium hydroxide or sodium hydroxide

Question 18

What decides if you get sub or elim reaction

Answer 18

sub- if the nucleophile is in aqueous solution (in water)
elim- if the nucleophile is in ethanol

Question 18

How are ethers synthesised?

Answer 18

• from haloalkanes and alkoxides

Question 19

How are ethers named?

Answer 19

• by assigning the longest carbon chain as the parent name
• prefixed by rhe alkocy sub (tke away -yl and add -oxy)

such as ethoxypropane, methoxypentane etc

Question 20

Properties of ethers

Answer 20

• bp lower than alcohols (no hydrogen bonding)
• low relative formula mass
• soluble in water (smaller ones only)
• highly flammable
• volatile

Question 21

Electrophilic addition

Answer 21

• alkenes undergo these with a variety of substances

Question 22

Hydrogenation

Answer 22

• catalytic addition of hydrogen
• cataclysed by nickel or palladium

Question 23

Halogenation of alkenes

Answer 23

• Br is the electrophile and undergoes heterolytic fission
• polarises at the double bond
• forms a intermediate bromonium ion
• Br ion attacjs intermediate and is acting as the nucleophile
• breaks delocalised ring to form haloalkane

Question 24

Hydrohalogenation

Answer 24

* addition of hydrogen halides to alkene * draw and check on slide 81 of U2 powerpoint

Question 25

Markovniov's rule | its not very catchy !!

Answer 25

When H-X is added onto an unsymetrical alkene the major product is the one where the hydrogen bonds to the carbon atom of the **double bond** that already has the **greatest numberr of hydrogen atoms attached to it**

Question 26

Hydration

Answer 26

* addition of water to alkene * step one produces a carbocation * step 2 the carbocation undergoes nucleophilic attack by a water molecule to give protonated alcohol * step 3 the protonated alcohol loses a proton to give final alcohol