One Chiral Center, Ipsenol

Since the nonequivalent methyl groups are each split by the vicinal CH proton, we expect to see two separate doublets. At 300 MHz, unfortunately, the pattern appears to be a classical triplet, usually an indication of a CH3—CH2 moiety—impossible to reconcile with the structural formula and the integration. Higher resolution would pull apart the middle peak to show two doublets. 

FIGURE 3.55 2-Methyl-6-methylen-7-octen-4-ol (ipsenol) in CDCT3 at 300 MHz. Titration with C6D6. The sample was a gift from PheroTech, Inc., Vancouver, BC, Canada. 

Note that the chiral center accounts for the fact that the protons of each of the two aliphatic methylene groups are also diastereotopic. As a result, the rather simple structure presents a challenge in assigning the spectrum to the given structure. 

It will help at this point to realize that the molecule consists of three spin systems with the insulation point at C-6 (see Section 3.5.2). The alkyl system consists of H-l, H-2, H-3, H-4, H-5, and H-9 an alkene system consists of H-7 and H-8 and another alkene system consists of H-10. The alkyl system accounts for the multiplets at the right of the spectrum, and the alkenes account for the multiplets at the left side. It will also help to reiterate that the protons of an alkyl CH2 group will be diastereotopic in the presence of a chiral center. As will be the protons of an alkene=CH2 group. 

It should now be apparent that the diastereotopic protons of each alkyl group CH2 group occur as a pair. One pair (H-3) is at 8 1.28 and 8 1.42 the other pair (H-5) is at 8 2.21 and 8 2.48. The two-proton multiplet at 8 1.80 will be discussed later. 

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