Skeletal formula Uncommon

A structural formula which is reduced (i.e., skeletal) in the sense that carbon atoms forming the backbone of the structure (esp. of an organic compound) are not labeled — they are shown simply as vertices — and hydrogen atoms are not shown at all (except those which are bonded to heteroatoms, or the exceptionally labeled carbon atoms) but heteroatoms are always labeled. (Labels of labeled hydrogen atoms are written next to labels of the atoms that they are bonded to, without a bond drawn between them. If there are several labeled hydrogen atoms bonded to the same atom then they are written as an H with a subscript for their number.) Carbon atoms which are (optionally) labeled tend to be in reactive extremities of the molecule, not the backbone of it.