3.2 synthesis

Question 1

what happens to the bonds in the reactant molecules when an organic reaction takes place

Answer 1

they are broken and bonds in the product molecules are made

Question 2

what is bond fission

Answer 2

the process of bond breaking

Question 3

what are the two types of bond fission

Answer 3

homolytic and heterolytic

Question 4

what is homolytic fission

Answer 4

this is when the electrons are separated equally, forming two neutral radicals

Question 5

what occurs during homolytic fission

Answer 5

each atom retains one electron from the sigma covalent bond and the bond breaks evenly

Question 6

when does homolytic fission usually occurs

Answer 6

when non polar covalent bonds are broken

Question 7

what do reactions involving homolytic fission tend to result in the formation of

Answer 7

a very complex mixture of products, making them unsuitable for organic synthesis

Question 8

what does heterolytic fission form

Answer 8

two oppositely charged ions

Question 9

when does heterolytic fission form

Answer 9

when one atom retains both electrons from the sigma covalent bond and the bond breaks unevenly

Question 10

when does heterolytic fission occur in relation to bonds

Answer 10

when polar covalent bonds are broken

Question 11

what can be used to represent the movement of electrons during bond fission and bond making

Answer 11

curly arrow notation

Question 12

what are attacking groups classified as in reactions involving heterolytic bond fission

Answer 12

nucleophiles or electrophiles

Question 13

what are nucleophiles

Answer 13

negatively charged ions or neutral molecules that are electron rich, and they are attracted toward atoms bearing a partial or full positive charge. they are capable of donating an electron pair to form a new covalent bond

Question 14

what are electrophiles

Answer 14

these are positively charged ions or neutral molecules that are electron deficient, and they are attracted toward atoms bearing a partial or full negative charge. they are capable of accepting an electron pair to form a new covalent bond

Question 15

which reaction types can be identified from a chemical equation

Answer 15

substitution
addition
elimination
condensation
hydrolysis
oxidation
reduction
neutralisation

Question 16

how can synthetic routes be devised

Answer 16

from a given reactant to final product

Question 17

what can be deduced by looking at the structural formula

Answer 17

the possible reactions of a particular molecule

Question 18

what is skeletal structural formula

Answer 18

neither the carbon atoms or any hydrogen attached to the carbon atoms are shown
the presence of a carbon atom is implied by a kink in the carbon backbone and at the end of a line

Question 19

what are haloalkanes

Answer 19

substituted alkanes in which one or more of the hydrogen atoms is replaced with a halogen atom

Question 20

what is a monohaloalkane

Answer 20

these contain only one halogen atom, can be classified as primary, secondary or tertiary according to the number of alkyl groups attached to the carbon atom containing the halogen atom.

Question 21

what do monohaloalkanes take part in elimination reactions to form

Answer 21

alkenes using a strong base, such as potassium, or sodium hydroxide in ethanol.

Question 22

what are the nucleophilic substitution reactions that monohaloalkanes take part in

Answer 22

• aqueous alkalis to form alcohols
• alcoholic alkoxides to form ethers
• ethanoic cyanide to form nitriles that can be hydrolysed to carboxylic acids

Question 23

what are the different mechanisms that monohaloalkanes can take part in nucleophilic substitution reactions by

Answer 23

Sn1 and Sn2

Question 24

what is the Sn1 mechanism

Answer 24

a nucleophilic substitution reaction with one species in the rate determining step. occurs in a minimum of two steps via a trigonal planar carbocation intermediate

Question 25

what is the Sn2 mechanism

Answer 25

a nucleophilic substitution reaction with two species in the rate determining step. occurs in a single step via a single five centred trigonal bipyramidal transition state

Question 26

what is a steric hindrance

Answer 26

the slowing of chemical reactions due to steric bulk. steric iss the arrangement of atoms in space

Question 27

what is inductive stabilisation

Answer 27

the stability of a molecule depending on the charge present on the atom and the groups bonded to the atom

Question 28

how can alcohols be prepared

Answer 28

from haloalkanes by substitution from alkenes by acid catalysed hydration aldehydes and ketones by reduction using a reducing agent such as lithium aluminium hydride

Question 30

what makes alcohols polar

Answer 30

the hydroxyl groups

Question 31

what are ethers regarded as

Answer 31

substituted alkanes in which a hydrogen atom is replaced by an alkoxy functional group

Question 32

what is the alkoxy functional group

Answer 32

-OR

Question 33

how can ethers be prepared

Answer 33

in a nucleophilic substitution reaction by reacting a monohaloalkane with an alkoxide

Question 34

why do ethers have lower boiling points than the corresponding isomeric alcohols

Answer 34

due to the lack of hydrogen bonding between the molecules

Question 35

why are larger ethers insoluble in water

Answer 35

due to their increased molecular size

Question 36

what are examples of soluble ethers

Answer 36

methoxymethane and methoxyethane

Question 37

why are ethers commonly used as solvents

Answer 37

they are relatively inert chemically and will dissolve many organic compounds

Question 38

how can alkenes be prepared

Answer 38

- dehydration of alcohols using aluminium oxide, concentrated sulfuric acid or concentrated phosphoric acid - base induced elimination of hydrogen halides from monohaloalkanes

Question 39

what are the electrophilic addition reactions that alkenes take part with

Answer 39

hydrogen to form alkanes in the presence of a catalyst halogens to form dihaloalkanes hydrogen halides to form monohaloalkanes water using an acid catalyst to form alcohols

Question 40

what does markovnikov's rule state

Answer 40

when a hydrogen halide or water is added to an unsymmetrical alkene, the hydrogen atom becomes attached to the carbon with the most hydrogen atoms attached to it already. this rule can be used to predict major and minor products formed during the reaction of a hydrogen halide or water with alkenes

Question 41

how can carboxylic acids be prepared

Answer 41

by oxidising primary alcohols using acidified permangenate, acidified dichromate, fehling's solution and tollen's reagent hydrolysing nitriles, esters or amides

Question 42

what are examples of reactions involving carboxylic acids

Answer 42

- formation of salts by reactions with metals or bases - condensation reactions with alcohols to form esters in the presence of concentrated sulfuric or concentrated phosphoric acid - reaction with amines to form alkylammonium salts that form amides when heated - reduction with lithium aluminium hydride to form primary alcohols

Question 43

what are amines

Answer 43

organic derivatives of ammonia in which one of more hydrogen atoms of ammonia has been replaced by an alkyl group. they can be classified as primary, secondary or tertiary according to the number of alkyl groups attached to the nitrogen atom

Question 44

what do amines react with the form salts

Answer 44

acids

Question 45

which type of amines display hydrogen bonding

Answer 45

primary and secondary

Question 46

why do primary and secondary amines have higher boiling points than isomeric tertiary amines

Answer 46

they display hydrogen bonding

Question 47

are amines weak bases, and what does this imply

Answer 47

yes, and it means they dissociate partially in solution.

Question 48

how do amines produce hydroxide ions

Answer 48

the nitrogen atom has a lone pair of electrons which can accept a proton from water

Question 49

what is the simplest member of the class of aromatic hydrocarbons

Answer 49

benzene

Question 50

why are benzene rings stable

Answer 50

due to the delocalisation of electrons in the conjugated system - this is why they do not take part in addition reactions

Question 51

how can bonding in benzene be explained

Answer 51

in terms of sp2 hybridisation, sigma and pi bonds, and electron delocalisation

Question 52

what is a benzene ring

Answer 52

this is when one hydrogen atom has been subsituted by a phenyl group

Question 53

what is the formula for a phenyl group

Answer 53

C6H5

Question 53

what is the formula for a phenyl group

Answer 53

C6H5

Question 54

what do reactions at benzene rings include

Answer 54

- halogenation by reaction of a halogen using alumium chloride or iron chloride for chlorination and aluminium bromide or iron bromide for bromination - alkylation by reaction of a haloalkane using aluminium chloride - nitration using concentrated sulfuric acid and concentrated nitric acid - sulfonation using concentrated sulfuric acid