6.2.4 Carbon-Carbon Bond Formation

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

contain the CN functional group

• 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)

haloalkane + NaCN/KCN → nitrile + NaCl/KCl • via ethanol

ethanol

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)

• 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)

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

carbonyl + HCN → hydroxynitrile • so either an aldehyde or ketone

• 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

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

• 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

amines • also hydroxynitriles too

nitrile + 2H2 → amine • Ni catalyst on the arrow

• 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)

carboxylic acids (and an ammonium salt)

nitrile + 2H2O + dilute aqueous acid (HCl) → carboxylic acid + ammonium salt • heat goes on the arrow

heat

• 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

alkylation and acylation

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

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

⌬ + C2H5Cl → ⌬-C2H5 + HCl • the alkyl chain attached to Cl leaves and joins the benzene ring instead • and the H replaced joins the Cl- left

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