Chapter 27: Amino Acids, Peptides and Proteins

Hydrogen Bonding

• H atoms on electronegative atoms, most importantly N-H or O-H systems are sufficiently electron poor that they will interact with lone pairs usually on other N or O atoms in an "extra" bonding interaction.

• The group that provides the H atom is sometimes referred to as the H bond donor.
• The group that provides the lone pair is sometimes referred to as the H bond acceptor.
• Hydrogen bonds are typically a lot weaker than normal covalent bonds.
• However, hydrogen bonds can affect the properties of molecules dramatically, e.g. boiling point of H₂O (100 ^oC) versus CH₄ (-162 ^oC)
• In proteins, the hydrogen bonding interactions of the backbone amide groups is critical to defining the structure.
• The following 3D CHIME image allows you to highlight the carbonyl C=O and N-H systems involved in hydrogen bonding interactions within a section of a protein.

Question   How many common functional groups can you think of that can be involved in hydrogen bonding as H atom donors ?