Question

Explain briefly this observation of chemical shift for these aliphatic protons indicated with an arrow. -0.5 ppm H2C

Answer 1

The chemical shift of indicated aliphatic pootons can be explained with the help of diamagnetic anisotropy Since the given compound is aromatic. because it is planar, as well as follow 4n+8 é Rule. magnetic field is directed perpendicular to the plane of the aromatic compound sie (Bo) conjugated H BoT t + 7 t The ring current is induced due to the delocalised in electrons of the aromatic ring, and this oing current creates its own magnetic field. It can be shown as - Bind. Bind. a) induced magnetic field. B. 1111111 (applied magnetic field) outside the ring induced magnetic field is in the same direction as the externally applied magnetic field and inside the ring the field (Bind.) is apposite of applied magnetic field (Bo) As a result, the net magnetic field outside the than the externally applied magnetic field alone and is less inside the ring ring is greater

Therefore, proton outside the ring experiences deshielding The zone cohere Bind, and be have fame direction called paramagnetic zone and come where Bind. and Bo have opposite direction, called diamagnetic zone. .. outer proton will be in paramagnetic zone and inner proton will be in diamagnetic zone. Proton outside the ring experiences deshielding, therefore have high chemical shift. and proton inside the ring experiences shielding i-e low chemical shift. 4--0,5 ppm ( diamagnetic zone I shielded)