Molecular Structure Determination


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8.1 Determination :  Use following spectral data to determine the structure of C7H8O

MS: 39 53 79 90 107
IR: 700 790
H[1]-NMR: 2.25 7.0
Solution:
Insert spectral data in proper text fields and calculate.
Step 1. Interpretation of common results
MS, IR and H[1]-NMR strongly indicates an aromatic.
MS --> disubst. ; IR (more specific) --> 1,3 disubst.
Step 2. Further investigation
C7H8O - C6H4 (disubst) = CH4O (possibly OH and methyl (CH3))
Verifyed by H[1]-NMR (Ph-CH3 Methyl H-shift) and MS (CH2-Ph-OH).
The result:This is a di-subst aromatic compound with a methyl and OH in 1,3 position.

8.2  Determination : Determine the structure of C9H10O2

MS: 43 65 91
IR: 690 740 1750
H[1]-NMR: 1.95 5.0 7.28


Solution:
Insert spectral data in proper text fields and calculate.
Step 1. Interpretation of common results
MS, IR and H[1]-NMR strongly indicates an aromatic.
MS --> Ph-CH2 ; IR --> monosubst. benz ; H[1]-NMR --> Aromatic H
What about these oxygens ?:
MS --> CH3-C=O ; IR --> Esters uconj. C=O & C-O ; H[1]-NMR --> C(=O)-O-CH (esters)
It must be an ester.
Step 2. Further investgation
C9H10O2 - phenyl(C6H5) = C3H5O2
By MS --> CH3C=O (MS) and H[1]-NMR --> C(=O)-O-CH , we can conclude that:
C3H5O2 = -CH2-C(=0)-O-CH3
The result:This is a mono-subst. aromatic compound: Ph-CH2-C(=0)-O-CH3


8.3 Determination : Use following spectral data to determine the structure of C5H8O3
MS: 29 45
IR: 1720 3000
H[1]-NMR : 11
C[13]-NMR(multiplicity) : 27.96(t) 29.71(q) 37.83(t) 178.26(s) 207.02(s)


Solution:
Insert spectral data in proper text fields and calculate.
Step 1. Interpretation of common results
MS, IR, H[1]-NMR and C[13]-NMR strongly indicate the attachment of a carboxyl group.
A C=O group (ketone) identifyed by C[13]-NMR (207.07), MS and IR.
Multiplicity: Carbon in both groups = singlets
Step 2. Further investgation
Multiplicity: 27.96(t) = CH2 37.83(t) = CH2 : 29.71(q) = CH3
The result: CH3-C(=O)-CH2-CH2-C(=O)OH


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