Polypeptide Bond Angles

#Biochemistry

Bond Rotation

• $\displaystyle \phi$ is the angle of rotation between the $\displaystyle \ce{N}$ and $\displaystyle \ce{C_{\alpha}}$ atoms
• $\displaystyle \psi$ is the angle of rotation between the $\displaystyle \ce{C}$ and $\displaystyle \ce{C_{\alpha}}$ atoms

Mnemonic

• The $\displaystyle \ce{C}$ carbonyl, $\displaystyle \ce{C_{\alpha}}$, $\displaystyle N$, and the carbonyl $\displaystyle \ce{O}$ are all coplanar due to conjugation by delocalization of the nitrogen lone pair. This means there is no variable angle of rotation between the $\displaystyle \ce{N}$ and carbonyl $\displaystyle \ce{C}$
• $\displaystyle \psi$ is a wave function in physics, and the carbonyl $\displaystyle \ce{O}$ looks like of like a stick figure's head, and so this stick figure "waves" his hand, which can only be between the carbonyl $\displaystyle \ce{C}$ and $\displaystyle \ce{C_{\alpha}}$
• $\displaystyle \phi$ is the Golden Ratio, which is goldeN, corresponding to the angle being between $\displaystyle \ce{N}$ and $\displaystyle \ce{C_{\alpha}}$