# IR Spectroscopy

 IR spectroscopy def
 measures molecular vibrations which can be seen as bond stretching/bending/combos of vibrational modes
 IR range in the unit of (cm-1)   max to min
 3,500 – 300
 give max to min of fingerprint region
 1500-400   (wont be tested but still good to know)
 given these frequencies : 2,800& 1,200 match to: C-H C-C why? (explain the trend)
 C-H: 2,800 C-C: 1,200   H bonded to any atom will have a higher frequency.
 given these frequencies : 1,645 & 1,200 match to: C=C C-C why? (explain the trend)
 C=C: 1,645 C-C: 1,200   as we add more bonds between carbon atoms the frequency increases.
 given these frequencies : 3,080& 1645 match to: =C-H C=C why? (explain the trend)
 =C-H:3,080 C=C: 1645 remeber any atom bonded to H will have the larger frequency
 given these frequencies : 2,200& 3300 match to: C=C =  C-H why? (explain the trend)
 C=C: 2,200 =  C-H: 3300   again the H
 Which compound would have the lower frequency in an IR spectrum: carbonyl vs a carbonyl in conjugation with double bonds?
 a carbonyl in conjugation with double bonds b/c the delocization of the pi electrons causes the  C=O bond to lose double bond character, causing to absorb near C-O frequencies (1,000-1250)
 give the peak for alcohol   is it (sharp/broad)?
 compare the frequency of an ether vs alcohol
 (OH) alcohol: 3300    (ROR) ether: 1050   remember H = higher frequency
 what is the frequency for the C=O (carbonyl bond)
 1700-1750
 using 1750 as a base : who will have a frequency above this value and at this value?   aldehyde vs ketone
 Above 1750: aldehyde (2,700) H-C=O has a Hydrogen & 1 R grp
 give an estimate  IR peak for: ketone carboxylix acid (2)
 ketone: 1700-1750 (carbonyl) c. acid will have 2 peaks: 1700-1750 (carbonyl) & 3300 (alcohol)
 give IR peak for amine (how does it differ from alcohol)
 3100- 3500 (same range as alcohol BUT has a sharp peak)
 Will Br2 have show up on an IR?
 no, for a compound to a frequency it must experience a dipole moment (aka an atom is attached to an electronegative atom.)   Br2 is symmetrical (and CCl4) and cant be detected by IR.
 give IR peak for C-H
 2800-3000 cm-1
 give IR peak for C-O
 1000-1300
 give IR peak for C-C
 this bond is too weak for IR ( C2 just like Br2 does not have dipole moment)
x

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