Splitting Patterns The Isopropyl Group

Spin-Spin Splitting in NMR Spectroscopy 555 Splitting Patterns The Ethyl Group 557 Splitting Patterns The Isopropyl Group 559 Splitting Patterns Pairs of Doublets 559 Complex Splitting Patterns 561 NMR Spectra of Alcohols 563... 

Splitting Patterns of the Ethyl Group and the Isopropyl Group... 

The NMR spectrum of isopropyl chloride (Figure 13 17) illustrates the appearance of an isopropyl group The signal for the six equivalent methyl protons at 8 1 5 is split into a doublet by the proton of the H—C—Cl unit In turn the H—C—Cl proton signal at 8 4 2 IS split into a septet by the six methyl protons A doublet-septet pattern is char acteristic of an isopropyl group... 

The signal of the methine proton in isobutyl methyl ether will be split into more than a septet, however, because in addition to being split by two methyl groups, it is coupled to the two protons in the methylene group. Thus, isobutyl methyl ether does not have the correct splitting pattern to be the answer. The correct answer is ethyl isopropyl ether. 

Use the splitting patterns to determine the numbers of adjacent protons, and assemble pieces of the molecule in a trial structure. Learn to recognize ethyl groups and isopropyl groups (and structures that resemble these groups) by their characteristic splitting patterns. 

The IR of Compound B shows a ketone absorption. The splitting pattern of the H NMR spectrum indicates an isopropyl group and indicates that the compound is a methyl ketone. 

Figure 3.16 The 90 MHz proton NMR spectmm of cumene, showing the characteristic isopropyl group splitting pattern. SDBS No. 1816HSP-00-081. (Courtesy of National Institute of Industrial Science and Technology, Japan, SDBSWebihttp //www.aist.go.jp/RIOBD/SDBS. Accessed 12/14/02.)...

The characteristic splitting patterns for ethyl, isopropyl, and tert-butyl groups. 

---