Distinguishing between an alkene and an aromatic compound by IR can be tricky. Often other information, such as the molecular formula, will tell you which is which. In the IR, both have sp2 CH peaks and a carbon-carbon double bond peak. One difference is the frequency of the latter - alkenes are usually around 1650 cm-1 (this peak may be pretty small, especially if the alkene is internal), while aromatic C=C's are at lower frequency - ~1600 cm-1 or less.
The examples for this exercise are cyclohexene and toluene. See if you can figure out which one is which.
Compound A
Click to expand any region:
| 4000 - 3200 cm-1 | 3200 - 2700 cm-1 | 2700 - 2000 cm-1 | 2000 - 1660 cm-1 | 1660 - 1400 cm-1 | 1400 - 900 cm-1 | 900 - 600 cm-1 |
Click to go to the IR data tables.
Click to go back to the exercise homepage.
Click to get:
| the molecular formula of this compound | the name of this compound | the structure of this compound |
Click to get an unknown.
Compound B
Click to expand any region:
| 4000 - 3200 cm-1 | 3200 - 2700 cm-1 | 2700 - 2000 cm-1 | 2000 - 1660 cm-1 | 1660 - 1400 cm-1 | 1400 - 900 cm-1 | 900 - 600 cm-1 |
Click to go to the IR data tables.
Click to go back to the exercise homepage.
Click to get:
| the molecular formula of this compound | the name of this compound | the structure of this compound |
Click to get an unknown.