It is the measurement of the distance between the peaks of a multiplet which arises after splitting. It is known as the coupling constant. It denoted by the J and its unit is Hertz. It is a useful tool in the measurement of the effectiveness of spin-spin coupling and predicting the protons NMR in complex structures. Types of coupling constant: 1) Geminal coupling: this type of coupling occurs between protons present on single carbon specifically in the terminal vinyl system. It ranges from 10-18 and denoted by ² But one condition is applied that the proton present should be non-equivalent. 2) Vicinal coupling: three bonds participate in coupling. It is denoted by ³J. It depends on the dihedral angle. Magnitude is 16Hz at 180⁰.  Newman’s projection is used to get a dihedral angle and then calculate it. 3) long-range coupling: it occurs when there are more than three bonds. Normally occurred within 4-5 bonds. But with polyalkynes, it is up to 9 bonds. It is denoted by >³J. Its range is 4-5.