6.2.4 Carbon-Carbon Bond Formation

Question 1

why is carbon-carbon bond formation important to reactions and mechanisms

Answer 1

• provides means of LENGTHENING THE C-CHAIN
• able to add side chains to benzene ring
• introduce new functional groups

Question 2

what are nitriles

Answer 2

contain the CN functional group

Question 3

why is forming a nitrile useful

Answer 3

• introduces a CN group
• SO INTRODUCING A C
• TO LENGTHEN THE CHAIN
• only way!!
• so provide a useful intermediate in mechanism pathways (can be reduced and hydrolysed)

Question 4

how do you form nitriles

Answer 4

haloalkane + NaCN/KCN → nitrile + NaCl/KCl

• via ethanol

Question 5

what are the conditions for the formation of a nitrile

Answer 5

ethanol

Question 6

what is the mechanism of forming a nitrile

Answer 6

nucleophilic substitution

• as substituting the halogen out of a haloalkane
• and doing it via nucleophile -:C≡N (MINUS SIGN AND LONE PAIR MUST GO ON THE C)

Question 7

explain the nucleophilic substitution mechanism for formation of nitriles

Answer 7

• the C-Cl bond in the haloalkane is polar, as Cl is δ- and C is δ+
• means that the lone pair on the negative -:CN ion is attracted to the δ+ C, and donates its electron pair here
• shown via arrow going from : to C
• the C-Cl bond breaks
• leaves CN in place of Cl, which is omitted to Cl- (can later react with whatever the specific CN compound was, e.g. forming NaCl)

Question 8

how else can a CN be added to a compound to elongate the chain

Answer 8

via the formation of a hydroxynitrile
- containing OH group on the same C as the CN
- increases the number of C in the chain via the addition of another C-C bond

Question 9

what is the basis of the formation of a hydroxynitrile

Answer 9

carbonyl + HCN → hydroxynitrile

• so either an aldehyde or ketone

Question 10

what are the actual reaction conditions of the formation of a hydroxynitrile, and why

Answer 10

• HCN is too poisonous to use
• so you use NaCN and H2SO4(aq) [as H+] instead
• improves safety
• but also increases the rate of reaction

Question 11

what is the mechanism of the formation of a hydroxynitrile

Answer 11

nucleophilic addition
- nucleophilic as still using a -:CN do donate a lone pair of e- to a δ+ C
- but this time addition, as you are breaking the carbonyl C=O bond to add it across

Question 12

outline the nucleophilic addition mechanism for the formation of a hydroxynitrile

Answer 12

• the C=O bond is polar, as C is δ+ and O is δ-
• so the lone pair on the -:CN is attracted to the δ+ C, and donates it
• shown as arrow going from : to C
• this breaks up the C=O bond, shown via arrow as well
• this leaves the O with a lone pair and a negative charge (O:-)
• the : lone pair on the O can react with δ+ H on a water molecule, shown as arrow going towards it
• the bond between the H and the rest of the water molecule then breaks, also shown
• means the H joins the O to form OH group
• and OH- is left behind

Question 13

what can a nitrile be reduced to

Answer 13

amines

• also hydroxynitriles too

Question 14

what is the equation for the the reduction of a nitrile

Answer 14

nitrile + 2H2 → amine

• Ni catalyst on the arrow

Question 15

what happens in the reduction of a nitrile

Answer 15

• the C≡N bond is broken
• and each H is added to the C and the N
• forming a straight chain alkane (C goes to CH2)
• with the NH2 amine group at the end (N goes to NH2)

Question 16

what are nitriles hydrolysed to form

Answer 16

carboxylic acids (and an ammonium salt)

Question 17

what is the equation for the hydrolysis of nitriles

Answer 17

nitrile + 2H2O + dilute aqueous acid (HCl) → carboxylic acid + ammonium salt

• heat goes on the arrow

Question 18

what are the conditions for the hydrolysis of nitriles

Answer 18

heat

Question 19

how are nitriles hydrolysis

Answer 19

• the main chain goes to form a COOH group at the end, kicking out the N
• the N forms NH4Cl salt, as reacts with the remaining Hs and Cl

Question 20

what are the two ways of forming a C-C bond on benzene rings

Answer 20

alkylation and acylation

Question 21

what is alkylation of benzene

Answer 21

the transfer of an alkyl group from a haloalkane to the benzene ring

Question 22

what conditions are necessary for the alkylation of benzene

Answer 22

a Friedel-Crafts catalyst
- so a halogen carrier
- like aluminium chloride AlCl3

Question 23

what is the equation for the alkylation of benzene

Answer 23

⌬ + C2H5Cl → ⌬-C2H5 + HCl

• the alkyl chain attached to Cl leaves and joins the benzene ring instead
• and the H replaced joins the Cl- left

Question 24

what is acylation

Answer 24

the addition of an acyl group
- which includes a carbon chain attached to a C=O

Question 25

what is needed for the acylation of benzene

Answer 25

an acyl chloride, and another halogen carrier catalyst, e.g. AlCl3 - can also be done with an acid anhydride, as interchangeable with an acyl chloride in terms of reactions

Question 26

what is the equation of the acylation of benzene

Answer 26

⌬ + acyl chloride → ⌬-ketone + HCl - e.g. ⌬ + C2H5C=O-Cl → ⌬-C=O-C2H5 + HCl - basically, the chlorine combines with the H in the benzene ring, and where they combine, are omitted as HCl

Question 27

why is the acylation of benzene ring useful

Answer 27

- useful in synthesis pathways - as the organic product is a ketone - so can react as one

Question 28

how can you further use the ketone formed via the acylation of benzene

Answer 28

- reduce with NaBH4 - to form an alcohol where the O is