Organic Chemistry - 3)b) Synthesis

Question 1

homolytic fission:

Answer 1

the breaking of a covalent bond to produce two free radicals

Question 2

heterolytic fission:

Answer 2

when a covalent bond breaks and both electrons in the bond move to one of the atoms

Question 3

what is formed as a result of heterolytic fission?

Answer 3

two oppositely charged ions

Question 4

what types of arrows are used in heterolytic fission?

Answer 4

full, double-headed arrows to show the movement of a pair of electrons

Question 5

why is heterolytic fission more likely to occur in polar molecules?

Answer 5

the electrons move to the more electronegative atom

Question 6

what is the term used to describe a positively charged carbon atom?

Answer 6

carbocation

Question 7

what is the term used to describe a negatively charged carbon atom?

Answer 7

carboanion

Question 8

what is a nucleophile?

Answer 8

(electron rich) neutral molecules or negatively charged ions that have at least one lone pair of electrons

Question 9

what is the role of a nucleophile?

Answer 9

the negatively charged ion or group is attracted to an electron-deficient centre where it donates its electron pair to form a new covalent bond

Question 10

what are three examples of nucleophiles?

Answer 10

H2O
NH3
OH-
halide ions

Question 11

what is an electrophile?

Answer 11

a neutral molecule or positively charged ion that are electron deficient

Question 12

what is the role of an electrophile?

Answer 12

attracted towards an area of high electron density with a negative or partial negative charge

Question 13

what are three examples of electrophiles?

Answer 13

H2O+
NO2+
SO3+

Question 14

what can be said about polar molecules?

Answer 14

they have both nucleophilic and electrophilic centres as they contain areas which are both positively and negatively charged

Question 15

what is a substitution reaction?

Answer 15

when an atom is replaced by another atom

Question 16

what is an addition reaction?

Answer 16

when two molecules join together to make one larger molecule

Question 17

what is an elimination reaction?

Answer 17

when a small molecule is removed from an organic compound

Question 18

how can alkenes be prepared?

Answer 18

by dehydration of alcohols

Question 19

what is Markinov’s Rule?

Answer 19

when a hydrogen halide or water is added to an asymmetric alkene, the hydrogen atom becomes attached to the carbon with the most hydrogen atoms attached to it already

Question 20

what can Markinov’s Rule be used to predict?

Answer 20

the major and minor products produced during the reaction of hydrogen halide or water with alkenes

Question 21

what can haloalkanes be used for?

Answer 21

anaesthetics
pharmaceuticals
flame retardants
solvents

Question 22

what type of haloalkane has the weakest bond?

Answer 22

iodoalkanes

Question 23

what type of haloalkane has the strongest bond?

Answer 23

fluoroalkanes

Question 24

what are the two main types of reactions which haloalkanes undergo?

Answer 24

substitution and elimination

Question 25

what is formed when haloalkanes undergo an elimination reaction?

Answer 25

alkenes

Question 26

what are the two type of substitution reactions associated with haloalkanes?

Answer 26

SN1 reactions and SN2 reactions

Question 27

what is the rate order for the slow reaction of SN1 reaction?

Answer 27

first order

Question 28

what is the overall rate order for the SN2 reaction?

Answer 28

second order

Question 29

why can't tertiary haloalkanes undergo SN2 reactions?

Answer 29

when a nucleophile attacks a primary haloalkane, it approaches from the side away from the halogen atom. This is impossible for a tertiary haloalkane as the back of the molecule is occupied by alkyl groups. This makes it impossible for nucleophiles to attack the haloalkane this way and means it has to undergo two-step process using the SN1 mechanism

Question 30

what is the term used to describe the effect in the previous answer?

Answer 30

steric hindrance