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#1 2010-11-14 19:42:54

orgopete
Administrator

Identify unknown (ethanol) from IR, NMR, and MS

http://www.curvedarrow.com/chem/ZZ2C2751B2.jpg


Just by surveying the data, it must be a low molecular weight compound. The IR suggests it has an OH group. From the NMR, it probably has six hydrogens. (A multiple of six could be present through symmetry, but that would increase the MW.) If it is six hydrogens, the there must be a CH3, a CH2 and an OH (from the IR). There is only one way this can be pieced together as a CH₂-group has two attachments and a CH₃ and an OH have one attachment.
CH₃- + -CH₂- + -OH → CH₃CH₂OH (mw 46)
NMR: triplet adjacent to a CH₂-group, a quartet indicating connected to oxygen from chemical shift and attached to a CH₃-group by adjacency rule. The OH is a singlet, exchangeable with D₂O.
IR has a big OH stretch, no C=O peaks, a C-O stretch at 1115 cm-1.
MS, parent ion 46, M-H (45), M-CH₃ (31, base peak, alpha cleavage).

The compound is ethanol (ethyl alcohol).

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