The following data is available from the
question.
Note
: Remember to cross
reference things to confirm.... eg. IR may show C=C, use NMR to
confirm that etc.
MS: M+ seen at 207 g/mol (odd MW suggests an odd number of N atoms, no Cl or Br isotope patterns - they require m and m+2 of 3:1 or 1:1 respectively).
EA:
Elemental analysis data for C and H (i.e. standard analysis) showed
69.54%
C, 6.76% N and 8.27% H (therefore there is 15.43% something else,
most
likely oxygen : remember oxygen can't be detected in a combustion
analysis). Use the MW from the mass spectra (above) to get
the partial molecular formula = C12H17N ?
(so that leaves 32). The missing piece is
consistent with 2 oxygen atoms (because 2 x 16 = 32) .... hence
C12H17NO2
From here we get the IHD
= 5
IR:
Confirms the presence of oxygen. There is a C=O at about 1732 cm-1
(high for a ketone) and an NH band between 3400-3300cm-1.
C-O stretches
can be seen around 1200cm-1. There are no -OH nor
triple bonds (CN or CC) absorbances.
13C
nmr: The proton decoupled spectrum shows a total of 10 peaks
indicating 10 types of C. By analysis of the chemical shifts, we have
types in
the
region for 1 x C=O above 160 ppm, four types of C=C at
120-140ppm (possibly ArC),
and 5 peaks between 0-60 ppm that are most likely from a hydrocarbon
portion, those nearer 60ppm are deshielded by something electronegative
such as O.
1H nmr: First of all we have 7 sets of peaks so we have 7 types of H showing up. After this, it's a good idea to tabulate the information to make sure you get it all correctly matched up:
|
|
|
|
|
m |
5 |
5 Ar-H = monosubstituted benzene, C6H5- |
4.2 |
q |
2 |
CH2 coupled to 3H, deshielded (by O ?) |
3.8 |
s |
2 |
CH2 not coupled, slightly deshielded |
2.9 |
t |
2 |
CH2 coupled to 2H, slightly deshielded |
2.5 |
t |
2 |
CH2 coupled to 2H, slightly deshielded |
1.9 |
s, brd |
1 |
NH or OH |
1.3 |
t |
3 |
CH3 coupled to 2H, hydrocarbon portion |
The pieces we have are C6H5-, CH3CH2O-,
-CH2CH2-, and -CH2-
, C=O and NH (2 end pieces, 4 middle pieces)
|
or
|
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 ?"
Major
errors: