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Test 1
Organic II
Question | Answer |
---|---|
As bond increases, wavenumber (IR) ________. | Increases |
As mass increases, wavenumber (IR) ________. | Decreases |
IR peak above 3000 | Sp2 C-H bond (unsaturated) |
IR peak below 3000 | Sp3 C-H bond |
Sharp IR absorption around 3300 with a smaller one about 2200 | Alkyne (C-H and C triple C) |
C-H IR _______ as bond goes from alkane -> alkene -> alkyne | Increases |
Steps for IR (with molecular equation) | 1. Unsaturation? 2. Possible structures/ look at key absorptions 3. Compare to IR/ build structure |
Put in order of high -> low wavenumber: N-H, C-H, O-H | O-H > N-H > C-H higher bond strength (electronegativity), greater wavenumber |
Equation for saturation for molecule with N | 2n+1=number of H needed to be saturated where n=C+N |
Amine IR | Low absorption (neither sharp or broad) around 3300-3500. Number of peaks in it are number of N-H bonds |
Equation for saturation with molecule with O | 2n+2 Ignore the O (n= C) |
Sharp, large IR absorption around 1700-1800 | Carbonyl group C=O |
Carboxylic acid IR | C=O absorption around 1700 and an OH frequency that often overlaps with C-H (around 2500-3300) |
Ester IR | C=O absorption around 1735-1800 with no OH absorption. Will be about 10 higher than ketones |
Aldehyde IR | "Fangs". Two sharp absorptions around 100cm-1 apart that are same intensity with one being around 1750cm-1. Second peak can be covered with sp3 C=H |
What to do if you don't know if 1H NMR signals are same? | Substitution test, see if molecule is homotopic/enantiotropic. If het/diast they are different. |
NMR splitting tells you | About the number of H's neighboring it. |
NMR signaling tells you | Number of equivalent H's on C |
Splitting names | Singlet, doublet, triplet, quartet, pentet, sextet, septet |
Splitting equation | Splitting=number of neighboring H + 1 |
NMR steps: | 1. Saturation if given molecule 2. Draw parts 3. Put together using NMR (greater chemical shift, closer to electronegative atoms/more sub C/double or triple bonds) |
What happens to chemical shift where a CH2 is surrounded by a Br on one side and a carbonyl group on the other? | The chemical shifts relating to each molecule (in response to Br and in response to carbonyl) are added minus a little |
NMR chemical shift around 7 | Aromatic ring |
Other giveaways for aromatic ring | LOTS of unsaturation (like C6H8), multiplet at high saturation |
If Ca - Cb J value = Cb - Cc J value in CaCbCc molecule, there is an NMR of: | An apparent sextet of a multiplet |
NH and OH frequently show up on NMR as: | 1H singlets |
Topicity if substitution test makes constitutional isomers: | Heterotopic, Hs are non-equivalent |
Topicity if substitution test makes conformational isomers: | Homotopic |
Topicity if substitution test makes enantiomers: | Enantiotopic |
Topicity if substitution test makes a chiral center: | Enantiotopic |
Topicity if substitution test doesn't make a chiral center: | Homotopic |
Topicity if substitution test makes diastereomers: | Diastereotopic, are not equivalent in NMR |
Number of signals in 13C NMR means: | Number of equivalent C's |
Common indicators of diastereotopic Hs: | 1. Alkene 2. Existing chiral center 3. Ring |
13C NMR shifts 100-160ppm | Aromatics and alkenes |
13C NMR shifts >180ppm | Aldehydes and ketones |
13C NMR shift 160-180ppm | Carboxylic acids |
13C NMR shift <80ppm | sp3 C |
In m/z, the peak showing mass of original molecule is called: | Parent (molecular ion) peak. M+ |
M/Z tells you: | Mass of whole molecule, masses of fragments (good at telling constitutional isomers apart) |
Fragmentation in m/z detects the fragment of radical cation with the: | Charge |
Alpha splitting: | Occurs with alcohols and carbonyls, C bonds will split on each side of the OH/C=O |
McLafferty's principle: | Certain type of m/z splitting that generated an EVEN m/z fragment due to an added H, needs a propyl chain to do, and produces an enol (alkene + alcohol) from a carbonyl group |