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Chem 30B > IR Spectroscopy > Flashcards

IR Spectroscopy Flashcards

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1
Q

spectroscopy

A

the use of electromagnetic radiation to probe matter

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2
Q

what does the amount of energy absorbed depend on

A

the change in the dipole moment

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3
Q

how does a large change in the dipole affect amount of energy absorbed

A

larger amount of energy is absorbed and it exhibits stronger absorption peaks

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4
Q

how are nonpolar bonds affected by infrared radiation

A

they do not absorb infrared radiation because there is no change in the dipole moment

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5
Q

how are relatively nonpolar bonds like C-C bonds affected by IR spectroscopy

A

absorb less energy and exhibit weak absorption peaks

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6
Q

acronym for remembering increasing —> decreasing electronegativity

A

FONClBrISCH

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7
Q

what is the dipole

A

difference in electronegativity

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8
Q

zone 1 range

A

3600 - 2800 cm-1

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9
Q

what groups does zone 1 include

A

carboxylic acids, alcohols, amines, C-H

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10
Q

what is zone 2 range

A

2300-2100 cm-1

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11
Q

what groups does zone 2 contain

A

alkynes, nitriles

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12
Q

what range does zone 3 have

A

1850 - 1600 cm-1

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13
Q

what groups does zone 3 contain

A

carbonyls, alkenes, benzene

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14
Q

zone 4 range

A

< 1400 cm-1

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15
Q

what groups does zone 4 have

A

C-O, -N, -X single bonds

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16
Q

characteristic of O-H and N-H vibrations

A

intense and broad signal around 3300 range in zone 1

17
Q

characteristics of C-H vibrations

A

triple peaked sharp medium signal near 2900-3000 range in zone 1

18
Q

how to tell the difference between IR spectroscopy absorption pattern for alcohols vs carboxylic acids

A
  • carboxylic acids have a broader O-H section due to extensive hydrogen bonding, while alcohols have both broad and sharp O-H sections
  • carboxylic acids have an intense zone 3 absorption for C=O, but alcohols do not
19
Q

characteristics of primary amine zone 1 absorption

A

twin set of peaks around 3360 and 3280 (associated with different vibrational modes available for hydrogen bonds) plus a sharp intense C-H spike around 3000

20
Q

characteristic zone 1 and 2 IR absorption for terminal alkyne

A

shark intense peaks at 3300 mark (or to the left of 3000 mark)

21
Q

characteristic zone 1 and 2 IR absorption for terminal alkenes

A

sharp little peak just to the left of 3000 mark, and steep three peaks just to the right of 3000 mark

22
Q

characteristics zone 1 IR absorption for alkane

A

nothing in zone 1, three sharp and intense peaks just to the right of 3000 mark

23
Q

characteristics of zone 1 and 2 IR absorption for aldehyde C-H bonds

A

nothing to the left of 3000, two distinct peaks around 2700 and 2800

24
Q

characteristics of zone 2 IR absorption for internal alkyne

A

weak dipole moment at 2050

25
Q

characteristics of zone 2 IR absorption for internal alkynes

A

sharp medium intensity peak at 2100

26
Q

characteristics of zone 2 IR absorption for terminal C N triple bonds

A

sharp intense peak around 2100

27
Q

zone 3 IR absorption characteristics for C=O

A

sharp intense peak

28
Q

how does resonance affect wave numbers

A

less double bond character means lower wave number

29
Q

what kind of resonance delocalization do aldehydes and ketones have

A

none

30
Q

what kind of resonance delocalization do esters have

A

minor resonance delocalization

31
Q

what kind of resonance delocalization do amides have

A

significant resonance delocalization of carbonyl p bond

32
Q

how does carbonyl bond strength compare to aldehydes/ketones/esters

A

it is weaker

33
Q

zone 3 IR absorption characteristics of alkenes

A

no C=C absorption for trans alkenes, but small sharp spike in 1600 range for cis alkenes; presence of a halide produces a large dipole with several intense sharp signals

34
Q

zone 3 IR absorption characteristics for benzene

A
  • overtones in 2000-1900 range (not in zone 1 or zone 2)
  • 2-3 peaks at 1600, 1400, and 1450 in zone 3 due to C-C stretching in aromatic ring
35
Q

how is IR spectroscopy used

A

absorption of IR radiation causes covalent bonds to change from a lower vibration state to a higher one

36
Q

function of IR spectroscopy

A

determining the kinds of functional groups in a molecule

37
Q

wavenumbers

A

the frequency of electromagnetic radiation expressed as the number of waves per cm, with units cm-1

Chem 30B (5 decks)

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