The Nuclear Overhauser Effect (NOE)

Question 1

Topicity

Answer 1

describes the symmetry relationship of two or more groups (or atoms) in a molecule that have identical connectivities (i.e., they are connected to the molecule in the same way).

Question 2

homotopic

Answer 2

if the groups (or atoms) are in identical environments, they are called homotopic. Homotopic groups are related to each other either by a bond rotation or an axis of rotation in the molecule

Question 3

enantiotopic

Answer 3

if the groups (or atoms) are in mirror image environments. Enantiotopic groups are related to each other by a reflective symmetry element (the most common being a mirror plane within the molecule).

Question 4

diastereotopic

Answer 4

if the groups (or atoms) are in different environments. Diastereotopic groups are not related by any symmetry elements or bond rotations.

Question 5

Homotopic and enantiotopic protons always appear at the same d,

Answer 5

, but, diastereotopic protons can appear at different shifts if diastereotopic protons are attached to the same carbon they can split each other (if they appear at different d).