I'm in Organic chemistry right now too, when we were doing 13C NMR this was my thought process:
First of all know what 13 CNMR does... it measures difference in alignment between two energy states. As a result, carbons in same chemical environment resonate at same frequency [SYMMETRY]. 13C NMR is key for analyzing the symmetry of the molecule when comparing to other specs...
1. Look at the number of peaks, number of peaks tells you about how many types of carbons. Compare the types of carbons to the mass spectrometry chemical composition to see symmetry [chemically identical carbons give same signal]. Make sure you recognize whether or not rotation makes an axis of symmetry (single bonds rotate). Be careful to see if there is any conjugation -- DMF is the classic example with 3 peaks in 13C NMR at room temperature, but two peaks at 150 degrees C
2. Look at the ranges:
200+: ketone, aldehyde (190ish)
200 - 150: unsaturated carbons next to O, C=O
- note even if a carbon is not double bonded to O directly, it can still be unsaturated, ex. C=C-O, the C next to O will appear in this range
- acid derivatives: carboxylic acid, ester, amide
150 - 100: unsaturated carbons, C=C, aromatic rings [note symmetry]
100 - 50: saturated carbons next to O, C-O
- note the 50 - 100 guideline is rough, C-O can appear at 45
50 - 100: saturated carbons, Me —- methyl groups will be here
You should also know:
More deshielded = more downfield = higher ppm —-> stronger frequency of radio wave needed to change alignment
Large chemical shift = downfield = high frequency of radio waves (shorter waves) = deshielded
small ppm = upfield = low frequency (longer waves) = shielded
You should also know that C13 NMR is not quantitative, integral does not equal the number of atoms
The key to those spectroscopy problems is being able to analyze multiple specs together and use data from them to piece together the molecule.
Right now we're on acid/base... anybody have any tips for that, it seems as though it's a lot to absorb especially with all the pKas