Isobutyl, sec-butyl, and tert-butyl groups are all types of alkyl groups in organic chemistry. The main difference between them lies in the way the carbon atoms are arranged in the group. Isobutyl has a branched structure with a methyl group attached to the second carbon atom, sec-butyl has a branched structure with a methyl group attached to the second carbon atom, and tert-butyl has a branched structure with a methyl group attached to the third carbon atom. These differences in structure can affect the reactivity and properties of organic compounds containing these groups.