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Flashcards in OChem Class 2 Deck (38)
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31

Mass Spectroscopy

- Used to determine the molecular weight of a compound
- Determines the elemental & isotopic composition of molecule

32

Infrared Spectroscopy (IR)

- Light in IR range causes different bonds to vibrate at distinct frequencies
- Indicates which function group is present (but not how many or where)
- Useful for distinguishing constitutional isomers not stereoisomers
- Peaks expressed as wavenumber (cm-1) in spectrum 1/λ)

33

Important Wavenumbers:
O-H
C=O
C=C
C≡N/ C≡C

O-H: 3200 - 3600
C=O: 1700
C=C: 1650
C≡N/ C≡C: 2100-2260

34

UV/Visible spectroscopy

- Indicates presence of conjugated pi system (alternating double and single bonds)
- more alternating bonds = longer the wavelength of light absorbed)

35

H-NMR (NMRI Spectroscopy)

Radiowaves determine information about H atoms in molecules

36

What are the 4 key features of H-NMR Spectrum?

1. # of signals (how many non-equivalent hydrogens)
2. Splitting pattern n+1 rule (# of non-equivalent neighbouring hydrogens)
3. Area under signal/ integration (#of hydrogens represented by each signal)
4. Chemical shift (ppm) (chemical environment of that hydrogen)

37

N+1 (splitting pattern) refers to...

# of peaks for a signal
1 - singlet
2 - doublet
3 - triplet
4 - quarter
5+ - multiplet

38

Chemical shift (δ)

δ indicates location of signal on H-NMR spectrum (expressed in ppm)

Downfield shift (high ppm)
- carbon attached to e- withdrawing group
- proton is deshielded

Upfield shift (low ppm)
- proton is shielded
- carbon attached to e- donating group

10 - 9: aldehyde
8-7: aromatic phenol
6-5: vinyl
5-2: alcohol
4-2: H-C-Y
2-0: alkyl