Question

What can I do to prepare for organic chemistry lab?

Answer 1

First off, you need a reference text. This is my recommendation for a cheap, yet very helpful text.
http://www.amazon.com/Techniques-Organic-Chemistry-Microscale-Williamson/dp/1429219564/ref=sr_1_2?s=books&ie=UTF8&qid=1428564666&sr=1-2

This also acts as a great and free reference, if your compound has already been analyzed:
http://sdbs.db.aist.go.jp/sdbs/cgi-bin/cre_index.cgi

Then, you need to be able to recognize the types of peak shapes (sharp and strong, sharp and weak, broad and strong, etc.) and what they might represent. For example, an O-H stretching vibration at `3500~3200 cm^-1` is often broad, like a bonding potential energy curve, and should be about medium or strong in a proper-concentration IR analyte solution. However, an N-H stretch potentially forms a more defined peak if it overlaps an O-H stretch in the same compound; it's less curved and a little more 'spiky'. (cf. 2-aminoethanol in SDBS.)

Some commonly recurring ones it helps to know/memorize/recognize, from Mohrig :
`3650~3550 cm^-1`: O-H stretches (alcohols) -- non-H-bonded
Broad, generally medium
`3550~3200 cm^-1`: O-H stretches (alcohols) -- H-bonded
Broad, generally strong
`3550~3150 cm^-1`: N-H stretches (amides, amines)
Generally broad, medium; occasionally is more defined if overlapping O-H stretch
`3310~3200 cm^-1`: C-H sp stretches
Generally strong
`3100~3000 cm^-1`: C-H sp2 stretches (alkenes + aromatics)
Generally medium to weak
`2990~2850 cm^-1`: C-H sp3 stretches
Generally medium to strong

`~2360 cm^-1`: CO2 (doublet)
Generally quite weak

{`1680~1620 cm^-1`: C=C stretches (saturated, alkene)
`1650~1600 cm^-1`: C=C stretches (conjugated, alkene)
`1620~1440 cm^-1`: C=C stretches (aromatics)}
Generally medium to weak
{`1740~1720 cm^-1`: C=O aldehyde stretches (saturated)
`1715~1680 cm^-1`: C=O aldehyde stretches (conjugated)}
Generally medium to weak
`1750~1705 cm^-1`: C=O ketone stretches (saturated)
`1700~1650 cm^-1`: C=O ketone stretches (conjugated)

`1480~1430, 1395~1340 cm^-1`: C-H sp3 bends