What is Bond line notation?

Bond line notation, also known as skeletal formula notation, is a shorthand way of representing the structure of organic molecules in organic chemistry. It is a simple and concise method used to depict the arrangement of atoms and bonds within a molecule.

In bond line notation:

Carbon atoms are not explicitly shown. Corners and endpoints of lines represent carbon atoms, with hydrogen atoms attached as necessary to satisfy the carbon valency (four bonds for carbon).

Hydrogen atoms directly bonded to carbon are usually not shown, except when necessary to avoid ambiguity or to indicate a specific functional group.

Heteroatoms (atoms other than carbon and hydrogen, such as nitrogen, oxygen, sulfur, etc.) are typically shown explicitly, along with their attached hydrogen atoms.

Lines represent covalent bonds between atoms. A single line (-) represents a single bond, a double line (=) represents a double bond, and a triple line (≡) represents a triple bond.

Lone pairs of electrons and formal charges are not shown in bond line notation.

By using bond line notation, chemists can quickly represent and convey the structure of complex organic molecules in a concise and easily understandable manner. It is widely used in chemical literature, textbooks, and research papers. However, it's essential to keep in mind that bond line notation doesn't provide information about the three-dimensional shape of molecules, which can be critical in understanding their reactivity and interactions in chemical reactions. For that, other 3D representation methods like wedge-dash notation or Newman projections are utilized.