Chem 351 F06 Final : Spectroscopy

Part 8: SPECTROSCOPY

The following data is available from the question.

Note : Remember to cross reference things to confirm.... e.g. IR may show C=C, use NMR to confirm that etc.

MS: M+ seen at 150 g/mol (no Cl or Br isotope patterns - they require m and m+2 of 3:1 or 1:1 respectively).

IR: There is no C=O near about 1700 cm^-1 but there is an -OH (3350 cm^-1). Absorbance near 1600cm^-1 suggests C=C possibly aromatic.

13C nmr: The proton decoupled spectrum shows a total of 8 peaks indicating 8 types of C. By analysis of the chemical shifts, we have types in the region of C=C at 125-150ppm (probably ArC, 4 types), 1 peak near 70 ppm (possibly a C with an electronegative oxygen attached) and then 3 peaks between 0-40 ppm that are most likely from a hydrocarbon portion.

1H nmr: The proton spectrum shows a total of 6 peaks indicating 6types of C. The peak at 3.5ppm is a CH2, possibly with an electronegative oxygen attached. Then peak at about 2.9ppm is a CH between 0-40 ppm that are most likely from a hydrocarbon portion.

d/ppm	multiplicity	integration	Inference
7-8	m	5	5 Ar-H , monosubstituted aromatic.
3.5	t	3	CH₂ coupled to 2H, deshielded (by O ?)
2.9	t	1	CH coupled to 2H, slightly deshielded
2.4	s (brd)	1	-OH
1.7	q	2	CH₂ coupled to 3H
1.2	d	3	CH₃ coupled to H

(m = multiplet, p = pentet, t = triplet, d = doublet, s = singlet)

The most significant structural information from this is :

peaks at 7-8 ppm indicates 5ArH therefore a monosubstituted aromatic C₆H₅-

Summary....
The MS indicated MW = 150
The IR showed the presence of OH
13C and H NMR gives C₆H₅- , CH₃CH, CH₂-, CH₂- and -OH
This is in agreement with a molecular formula of C₁₀H₁₄Owith MW = 150 (yes!)

Altogether...

Chemical shift implies HOCH₂-

The coupling of this CH2 requires that it be HOCH₂CH₂-

Therefore the Ph and this HOCH₂CH₂ group are attached to the CH₃CH group

The final step should always be to check what you have drawn. The easiest thing to check is usually the coupling patterns you would expect to see, and the chemical shifts of each unit. You should be asking yourself : "Does my answer give me what the H-nmr shows ?"