The n+1 rule links the splitting of a 1H NMR peak to its neighbours:H atoms with n H atoms on the adjacent carbon(s) give a peak split into n + 1 lines So:
• 0 adjacent H: singlet (1 line)
• 1 adjacent H: doublet (2 lines)
• 2 adjacent H: triplet (3 lines)
• 3 adjacent H: quartet (4 lines)The splitting tells you about the neighbours, not about the H atoms in the peak itself. Count the H atoms on all adjacent carbons that are in a different environment. Do not count H atoms on O, which usually do not couple.Worked example 1: chloroethane, CH3CH2Cl
CH3: the adjacent CH2 has 2 H, so n = 2, giving a triplet.
CH2: the adjacent CH3 has 3 H, so n = 3, giving a quartet.Worked example 2: 2-chloropropane, CH3CHClCH3
The two CH3 groups are equivalent (6 H). Each is next to the CH, which has 1 H, so n = 1: a doublet.
The CH is next to two CH3 groups, 6 H in total, so n = 6: it is split into 7 lines.Worked example 3: propanone, CH3COCH3
Each CH3 is next to the C=O carbon, which has no H, so n = 0: a singlet.Working backwards: a quartet tells you the H atoms are next to a CH3 (methyl) group, a triplet tells you they are next to a CH2 group, and a doublet tells you they are next to a CH group.
• 0 adjacent H: singlet (1 line)
• 1 adjacent H: doublet (2 lines)
• 2 adjacent H: triplet (3 lines)
• 3 adjacent H: quartet (4 lines)The splitting tells you about the neighbours, not about the H atoms in the peak itself. Count the H atoms on all adjacent carbons that are in a different environment. Do not count H atoms on O, which usually do not couple.Worked example 1: chloroethane, CH3CH2Cl
CH3: the adjacent CH2 has 2 H, so n = 2, giving a triplet.
CH2: the adjacent CH3 has 3 H, so n = 3, giving a quartet.Worked example 2: 2-chloropropane, CH3CHClCH3
The two CH3 groups are equivalent (6 H). Each is next to the CH, which has 1 H, so n = 1: a doublet.
The CH is next to two CH3 groups, 6 H in total, so n = 6: it is split into 7 lines.Worked example 3: propanone, CH3COCH3
Each CH3 is next to the C=O carbon, which has no H, so n = 0: a singlet.Working backwards: a quartet tells you the H atoms are next to a CH3 (methyl) group, a triplet tells you they are next to a CH2 group, and a doublet tells you they are next to a CH group.