Unformatted text preview: 1 6-45 is loss of methyl. Mass spectrum: Molecular ion at base peak at Infrared spectrum: The broad peak at cm-l is OH; thymol must be an alcohol. The peak at cm-l suggests an aromatic compound. spectrum: The singlet at is OH; it disappears upon shaking with D20. The 6H doublet at and the IH multiplet at are an isopropyl group, apparently on the benzene ring. H singlet at is a methyl group, also on the benzene ring. Analysis of the aromatic protons suggests the substitution pattern. The three aromatic hydrogens confinn that there are three substituents. The singlet at is a proton between two substituents (no neighboring H's). The doublets at and are ortho hydrogens, splitting each other.
ISO; 135, M - 15, 3 500 1 620 NMR (') 3 .2 (') 4.8 A3 (') 2.3 (') 1 .2 Several isomeric combinations are consistent with the spectra (although the single H giving suggests that either or is the OH group-an OH on a benzene ring shields hydrogens ortho to it, moving them upfield). The structure of thymol is:
8 6 .5 CH3 The final question is how the molecule fragments in the mass spectrometer: H H CH3 'CI CH3 I + OH OH OH + .. I hI hCH3 � ¢r CH3 CH3 CH3 mlz resonance stabilization of this benzylic cation includes fonns with positive charge on three ring carbons and on oxygen (shown)
.. .. .. �Y Y
X Z (5 6 . 75 (5 7. 1 (5 6 .5 + CH] ¢r:;� thymol + • 1 35 3 60 ...
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