Polynuclear Aromatics

Napthalene

Naphthalene: nomenclature: Mono substituted:α-1- β- 2- Special names:

Heat of hydrogenation is –61 Kcal/mole lower than predicted (resonance stabilization energy). Benzene is –36 Kcal/mole lower than predicted =  the second aromatic ring is less stable.

Naphthalene, reactions: 1) oxidation:

Note: Because naphthalene is sensitive to oxidation, you cannot make naphthoic acids via oxidation of a side chain.

2. Reduction:

3. Electrophilic Aromatic Substitution:

Electrophilic aromatic substitution (cont.)

Why is EAS in naphthalene mostly to the alpha-position?

EAS in syntheses of substituted naphthalenes: Alpha-substitution via halogenation or nitration.

Beta-substitution via high temp sulfonation or Friedel-Crafts acylation in nitrobenzene.

EAS in substituted naphthalenes: a)With an activating group to EAS in the alpha position  4- plus a little 2- in the beta position  1- b)With a deactivating group to EAS  the other ring, usually alpha ( 5- & 8- )

Haworth Synthesis of naphthalene

Substituted naphthalenes via Haworth synthesis:

Oxidation:

Reduction:

EAS in anthracene or phenanthrene yields mixtures and is not generally useful. For example, in sulfonation:

Haworth synthesis of anthracene

Haworth synthesis of phenanthrene