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Disubstituted Benzene Names

Disubstituted Benzene Names. To indicate relative position on a benzene ring: ortho- (o) on adjacent carbons (1,2) meta- (m) separated by one carbon (1,3) para- (p) separated by two carbons (1,4). Disubstituted Benzenes.

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Disubstituted Benzene Names

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  1. Disubstituted Benzene Names To indicate relative position on a benzene ring: • ortho- (o) on adjacent carbons (1,2) • meta- (m) separated by one carbon (1,3) • para- (p) separated by two carbons (1,4)

  2. Disubstituted Benzenes Ortho, meta, and para can also describe reaction patterns (“occurs at the para position”) Label positions on the ring relative to the –X substituent: Reaction at the para position:

  3. Benzene with more than Two Substituents Choose numbers to get lowest possible values List substituents alphabetically with hyphenated numbers Names like “toluene” and “phenol” can serve as root name(note that C1 is fixed by the -CH3 or OH group)

  4. 15.3 Structure and Stability of Benzene Recall the reaction of regular alkenes with Br2. You get rapid addition at RT to give the dibromo cmpd: alkenepi bondsarereactive But under these conditions, benzene gives no reaction: Benzenepi bondsunreactive!

  5. 15.3 Structure and Stability of Benzene Benzene will react with Br2 to give bromobenzene, but it requires heat and iron catalyst (slow). This is substitution rather than addition as seen with regular alkenes, suggesting that benzene has special stability

  6. Benzene - Aromatic Stablility Heats of hydrogenation demonstrate the extra stability of the benzene molecule. hypothetical actual

  7. Benzene’s Unusual Structure • All its C-C bonds are the same length: 139 pm This is halfway between regular C-C single bond (154 pm) and C-C double bond (134 pm) • Electron density in all six C-C bonds is identical • Structure is planar, hexagonal with 120° bond angles

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