A -CH3 group, also known as a methyl group, indicates the presence of an alkyl group in an organic molecule. The presence of a methyl group can influence a molecule's properties and reactivity.

Here's what a -CH3 group signifies:

• Hydrophobicity: Methyl groups are nonpolar and hydrophobic, meaning they tend to repel water. Adding methyl groups to a molecule increases its hydrophobicity.
• Steric Effects: Methyl groups are relatively small but can still influence the shape and reactivity of a molecule due to steric hindrance (the physical blocking of a reaction site).
• Reactivity: Methyl groups themselves are generally not very reactive, but their presence can affect the reactivity of nearby functional groups.
• Nomenclature: The presence of a methyl group is denoted by "methyl-" in the IUPAC name of the organic compound. For example, methane, methylbenzene, etc.

Methylation, the addition of a methyl group, is a crucial process in biochemistry, affecting gene expression and protein function.