CHAPTER THIRTEEN Spectroscopy H3C H3C H3C H2 Hexamethylbenzene 2, 3-Dimethyl-2-butene Chemical shift (6),ppm: Table 13.1 collects chemical-shift information for protons of various types. Within each type, methyl(CH3)protons are more shielded than methylene(CH2) protons, and methylene protons are more shielded than methine(Ch) protons. These differences are mall--only about 0.7 ppm separates a methyl proton from a methine proton of the same type. Overall, proton chemical shifts among common organic compounds encompass a range of about 12 ppm. The protons in alkanes are the most shielded, and O-H pro- tons of carboxylic acids are the least shielded TABLE 13.1 Chemical Shifts of Representative Types of Protons Chemical shift(6) Chemical shift(6) Type of proton ppm* Type of proton ppm* 0.9-1.8 2.2-2.9 1.6-2.6 3.1-4.1 2.1-2.5 2.7-4.1 H-C-C≡N 3.3-3.7 2.5 2.3-2.8 H-NR 4.5-6.5 6.5-8.5 H— H-oc- 10-1 *Approximate values relative to tetramethylsilane; other groups within the molecule can cause a proton The chemical shifts of protons bonded to nitrogen and oxygen are temperature- and concentration- Back Forward Main MenuToc Study Guide ToC Student o MHHE WebsiteTable 13.1 collects chemical-shift information for protons of various types. Within each type, methyl (CH3) protons are more shielded than methylene (CH2) protons, and methylene protons are more shielded than methine (CH) protons. These differences are small—only about 0.7 ppm separates a methyl proton from a methine proton of the same type. Overall, proton chemical shifts among common organic compounds encompass a range of about 12 ppm. The protons in alkanes are the most shielded, and O±H pro￾tons of carboxylic acids are the least shielded. Chemical shift (), ppm: CH3 CH3 H3C CH3 H3C H3C Hexamethylbenzene 2.2 C CH3 CH3 H3C H3C C 2,3-Dimethyl-2-butene 1.7 496 CHAPTER THIRTEEN Spectroscopy TABLE 13.1 Chemical Shifts of Representative Types of Protons *Approximate values relative to tetramethylsilane; other groups within the molecule can cause a proton signal to appear outside of the range cited. † The chemical shifts of protons bonded to nitrogen and oxygen are temperature- and concentration￾dependent. Type of proton H±C±R W W H±C±CœC W W H±C±CPN W W H±CPC± H±C±C± W W O X H±C± O X H±C±Ar W W H±Ar H±CœC ± ± W Type of proton H±C±NR W W H±C±Cl W W H±C±Br W W H±C±O W W H±OC± O X H±NR H±OAr H±OR 0.9–1.8 Chemical shift (), ppm* 1.6–2.6 2.1–2.5 2.1–3 2.5 2.3–2.8 4.5–6.5 6.5–8.5 9–10 2.2–2.9 Chemical shift (), ppm* 3.1–4.1 2.7–4.1 3.3–3.7 1–3† 0.5–5† 6–8† 10–13† Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website