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MCAT > Spectroscopy > Flashcards

Spectroscopy Flashcards

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MCAT flashcards
1
Q

What does IR spectroscopy stand for?

A

Infrared

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2
Q

What does IR spectroscopy measure?

A

Molecular vibrations - bending and stretching bonds

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3
Q

What wavelengths do IR spectroscopy measure?

A

700nm to 1mm

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4
Q

What is wavenumber and what units is it measured in?

A

1/wavelength, cm-1

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5
Q

What is the relationship between wavenumber and frequency?

A

Directly proportional

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6
Q

What wavenumbers do IR spectroscopy measure?

A

4000-400cm-1

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7
Q

Does symmetric stretch show up on IR spectroscopy and why?

A

No because there is no net change in dipole

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8
Q

Does asymmetric stretch show up on IRB spectroscopy and why?

A

Yes because there is a change in net dipole

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9
Q

What wavenumbers characterize the fingerprint region?

A

1500-400cm-1

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10
Q

What is the fingerprint region?

A

Specific absorbance pattern characteristic to each molecule

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11
Q

What is the frequency and shape of the -OH peak in alcohol?

A

Wide (broad) peak at 3300

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12
Q

What is the frequency and shape of the -OH peak in carboxylic acid?

A

Wide (broad) peak at 3000

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13
Q

What is the frequency and shape of the C=O peak?

A

Sharp peak at 1700

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14
Q

What is the frequency and shape of the -NH peak?

A

Sharp peak at 3300

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15
Q

What peak is broad at 3300?

A

Alcohol OH

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16
Q

What peak is broad at 3000?

A

Carboxylic Acid OH

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17
Q

What is the carboxylic acid OH lower than alcohol OH peak?

A

Carbonyl draws some electron density in carboxylic acid

18
Q

What peak is sharp at 1700?

A

Carbonyl

19
Q

What peak is sharp at 3000?

A

N-H

20
Q

Do higher order bonds have higher or lower absorption frequencies?

A

Higher

21
Q

What is plotted in IR Spectroscopy?

A

Wavenumber on x and %transmittance on y

22
Q

What does UV spectroscopy stand for?

A

Ultraviolet

23
Q

What does UV spectroscopy measure?

A

Absorbance of a sample dissolved in inert solution when UV light is passed through it

24
Q

What is plotted in UV spectroscopy?

A

Absorbance vs wavelength

25
Q

What causes absorbance of UV light?

A

Electronic transitions between orbitals

26
Q

Does conjugations increase or decrease the wavelength of maximum absorbance and why?

A

Increase due to lower energy of transition due to lower energy gap between HOMO and LUMO

27
Q

HOMO

A

Highest occupied molecular orbital

28
Q

LUMO

A

Lowest unoccupied molecular orbital

29
Q

What is the relationship between wavelength and frequency?

A

Inversely proportional

30
Q

What is the units for chemical shift?

A

Parts per million (ppm)

31
Q

Chemical shift of 0

A

TMS reference line

32
Q

Which way does a downfield shift move?

A

Left

33
Q

Which way does an upfield shift move?

A

Right

34
Q

What does the height of a peak in NMR spec represent?

A

Proportional to the number of protons

35
Q

How do electronegative atoms affect chemical shift and why?

A

Deshield protons by drawing away electron density and move the peak downfield

36
Q

Which direction does deshielding move the peak?

A

Downfield, left

37
Q

Deshielding

A

Electronegative atoms draw electron density from the proton and move the chemical shift downfield, left

38
Q

Spin-spin coupling

A

Two protons that are not magnetically identical within three bonds of one another

39
Q

How many peaks are present in spin-spin coupling?

A

n+1 where n is the number of protons less than 3 bonds away from the proton of interest

40
Q

What is the chemical shift of an aldehyde proton?

A

9-10ppm

41
Q

What is the chemical shift of a carboxylic acid proton?

A

10.5-12ppm

42
Q

What is the chemical shift of a benzene proton?

A

6-8.5

MCAT (31 decks)

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