3.3 Alkynes
57
3.3 Alkynes
Assignment
Range
Comments
C– – – C
65–85 ppm
Coupling constant, 2 J HC– –
–13 C ≈50 Hz; often
leading to unexpected signs of signals in
DEPT spectra and unexpected signals in 2D
heteronuclear correlation spectra
C–(C– – – C)
0–30 ppm
H–(C– – – C)
1.5–3.0 ppm
Coupling constants: | 4 J CH–C– –
– CH | ≈3 Hz
| 5 J CH–C– –
– C–CH | ≈3 Hz
CH 3 –(C– – – C)
≈1.8 ppm
CH 2 –(C– – – C)
≈2.2 ppm
CH–(C– – – C)
≈2.6 ppm
H–C(– – – C) st
3340–3250 cm -1 Sharp, intensive
C– – – C st
2260–2100 cm -1 Sometimes very week
Molecular ion
Weak, in the case of 1-alkynes up to C 7 often
absent
Fragments
[M-1] + often significant
Rearrangements
Extensive rearrangements, not very
characteristic
C– – – C π π* < 210 nm
(log ε 3.7–4.0)
Isolated double bonds;
for highly substituted double bonds often
several weak bands <240 nm
13 C
1 H
IR
MS
UV