Illustrate Hydrogen Bonding: Amino Acids

[MightyMan11]

Homework Statement

The following structures illustrate hydrogen bonding interactions between amino acid side chains and/or backbone atoms within a protein structure. In which of the following figures are the structures and hydrogen bonding completely correct?

Homework Equations

The Attempt at a Solution

Firstly, I know that structure 4 is wrong (does not involve hydrogen).
A quick glance at my textbook shows that the amino acid with the configuration of -OH shown in structure 3 does not exist, eliminating 3.
However, I am stuck at 1 & 2 as they seem both correct.
Any insight would be greatly appreciated.

 

[Ygggdrasil]

Which atoms have hydrogen capable of forming hydrogen bonds?

 

[MightyMan11]

Ah.
The electronegativity difference between sulphur and hydrogen seems to low to have a hydrogen bond.
That would leave structure 1 (also nitrogen and hydrogen have an electronegativity difference that is high enough to create a H-bond).

Thank you,
Ygggdrasil

 

[Ygggdrasil]

A good rule of thumb is that only hydrogens bonded to fluorine, nitrogen, or hydrogen atoms are capable of participating in hydrogen bonds.