types of reactions in organic chemistry

Question 1

substitution reactions

Answer 1

chemical reaction in which an atom or a group of atoms in a molecule is replaced by another atom or group of atoms

Question 2

outline mechanism of monchlorination of methane

Answer 2

1. initiation
   -a chlorine molecule is broken into 2 chlorine fee radicals in the presence of uv light (homolytic fission)- example of photochemical reaction
2. propogation
   -chlorine atom attacks a methane molecule to form hydrogen chloride and a methyl free radical.
   3- propagation pt 2
   - methyl free radical attacks a chlorine molecule to form chloromethane and a chlorine atom, this is used again in step 2 thereform this is a chain reaction
3. all of these free radicals combine to form a non free radical molecule

Question 3

mechanism

Answer 3

the detailed step by step description of how the overall reaction occurs

Question 4

homolysis/homolytic fission

Answer 4

the splitting of a pair of atoms so that each pf the two products end up with one electron from the pair of electrons that had been involved in bonding them

Question 5

free radical

Answer 5

any atom or group of atoms with an unpaired electron

Question 6

chain reaction

Answer 6

is a reaction that continues on and on because a product from one step of the reaction is a reactant for another step of the reaction

Question 7

evidence for the mechanism of monochlorination of methane

Answer 7

1. reaction takes place in UV light- the effect of UV light suggests a free radical mechanism in which Cl2 is broken down into two Cl free radicals by light
2. for every photon of light, thousands of chloromethane molecules are produced-suggests a chain reaction is taking place
3. ethane is found in the products- methyl free radicals must be present. two methyl free radicals must be combining to form ethane
4. adding a source of free radicals eg tetramethyl lead increases ror- only a reaction involving free radicals would be affected by adding a substance that provides free radicals ie that promotes a chain reaction
5. addition of an inhibitor s uch as oxygen slows down rate of reaction- implies a chain reaction is taking place, inhibitor is combining with free radicals to stop chain formation

Question 8

use of fully halogenated alkanes

Answer 8

flame retardants

Question 9

formation of an ester is what type of reaction

Answer 9

esterification, condensation and substitution

Question 10

what is reverse reaction of esterification

Answer 10

hydrolysis

Question 11

saponification

Answer 11

is the base hydrolysis of esters

Question 12

word equation of saponification

Answer 12

glycerol tristearate + sodium hydroxide -> sodium stearate and glycerol

Question 13

addition reaction

Answer 13

is one in which two or more molecules react together to form a single molecule

Question 14

uses of chloroethane

Answer 14

dentistry

Question 15

uses of 1,2-dichloroethane

Answer 15

PVC in windows etc

Question 16

hydrogenation of vegetable oils

Answer 16

the addition of a hydrogen atom across a double bond in a saturated fat in the presence of a nickel catalyst

Question 17

mechanism of the reaction between ethene and bromine

Answer 17

1. polarisation
   the double bond in ethene induces polarity in bromine molecule
2. homolytic fission
   induced polarity becomes so great that bromine splits into Br+ and Br-
3. carbonium ion formation.
   Br+ attacks the C2H4 molecule in order to gain 2 electrons (to fill its outer energy level), Br+ forms covalent bond with one of the carbon atoms leaving the other with a positive charge, the positively charged carbon atom is known as a carbonium ion (cyclic bromonium may be formed)
4. Ionic addition
   Br- then attacks carbonium ion (ionic addition becaiser ions add across the c=c bond)

Question 18

evidence for the mechanism of reaction between ethene and bromine

Answer 18

evidence comes from observation of what happens when ethene reacts with bromine in water that contains sodium chloride

1-bromo2-chloroethane is formed ; formed when carbonium ion is attacked by cl- ion therefore is evidence for the existence of carbonium ion as an intermediate in mechanism

2-bromoethanol is formed : formed when carbonium ion is attacked by the water molecule

Question 19

polymers

Answer 19

long chain molecules made by joining many small molecules eg polythene

Question 20

repeating unit

Answer 20

the part of a polymer whose repetition produces the complete polymer chain except for the end groups

Question 21

elimination reaction

Answer 21

is one in which a small molecule is removed from a larger molecule to leave a double bond in the larger molecule

Question 22

primary alcohol + oxidising agent=?

Answer 22

aldehyde

Question 23

secondary alcohol + oxidising agent =?

Answer 23

ketones

Question 24

what is fehlings solution made up of

Answer 24

fehlings a- copper sulfate in water

fehlings b- potassium sodium tartrate and sodium hydroxide