In the tertiary structure of hair, cross links between the R groups of cysteine are known as

In the tertiary structure of proteins (including keratin in hair), disulfide bonds form between the sulfur atoms in cysteine amino acid R groups. These covalent bonds provide structural stability and are responsible for hair's strength. Carbon-carbon bonds don't specifically link R groups, hydroxide is not a bond type, and dihydride is not a relevant term.