Chapter 18, Problem 50PP

Interpretation Introduction

Interpretation: Constitutional isomer of xylene should be identified to undergo a Birch reduction which produces a compound that should exhibit five signals in its ${}^{\text{13}}\text{C NMR}$ spectrum

Concept introduction:

• The carbon atoms of aromatic rings typically produce signals in the range of 100-150ppm in ${}^{\text{13}}\text{C NMR}$ spectrum. The number of signals is very helpful in determining the specific substitution for substituted aromatic ring.
  • Birch reduction converts aromatic compound having benzoid ring in to a product 1, 4-cyclohexa diene. The product having hydrogen atoms attached on opposite end of the molecule
  • Birch reduction is the reduction of aromatic rings with sodium , potassium or lithium and an alcohol in liquid ammonia
  • When benzene with an electron donating group such as alkyl group is treated with Birch reduction, the carbon atom connected to the alkyl group is not reduced. Electron   donating effect destabilizes the radical anion.
  • When an electron withdrawing groups are used, different regiochemical outcome is observed. Electron withdrawing   effect stabilizes the intermediate.