The sex attractant of the codling moth gives an IR spectrum with a broad signal
ID: 479834 • Letter: T
Question
The sex attractant of the codling moth gives an IR spectrum with a broad signal between 3200 and 3600 cm-1 and two signals between 1600 and 1700 cm-1. In the mass spectrum of this compound, the molecular ion peak appears at m/z = 196, and the relative abun- dances of the molecular ion and the (M+1)+• peak are 27.2% and 3.9%, respectively.
(a) What functional groups are present in this compound?
(b) How many carbon atoms are present in the compound?
(c) Based on the information given, propose a molecular formula for the compound.
Explanation / Answer
Answer:
1) Determination of Molecular formula from Mass spectrum.
a) M+ (molecular ion peak) = 196 hence molecular mass of unknown compound is 196.
b) "Rule of 13 " : 196 / 13 gives quotient = 15 and remainder = 1 hence hydrocarbon structure is C15H16.
I.R. shows a broad signal between 3200 - 3600 cm-1.indicative of -OH stretch. (even molar mass rulled out the possibility of N by Nitrogen rule.)
and 2 signals in the region 1500 - 1600 cm-1 suggestive of carbonyl C=O stretch probably in conjugation with aromatic sp2 C=C.
Taking into consideration that there is posibility of -OH and C=O functionality we need to adjust formula for 2 O atoms. 2 O adjusted by removinf C2H8 from C15H16 i.e. C15H16 - C2H8 = C13H8O2.
M.F. of unknown = C13H8O2.
c) # Unsatuarion sute determination
M.F. C13H8O2. n = 13 and m = 8
# of unsaturation sites = [(2n+2) - m] / 2 = [(2x13+2) - 8] = 20/2 = 10.
10 unsaturation sites can account for 2 phenyl rings + 1 or 2 C=O group and or a ring and/or C=C vinyl.
a) Phneyl group, vinylic C=C, carboxyic -COOH or C=O + phenolic or alcoholic -OH these functional groups possibly present.
b) # of C atoms are 13.
c) Molecular formula proposed ic C13H8O2.
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