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MCAT Organic Chemistry > Spectroscopy > Flashcards

Spectroscopy Flashcards

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1
Q

measures the energy differences between the possible states of a molecular system by determining the frequencies of electromagnetic radiation absorbed by the molecules; types include infrared, ultraviolet, and nuclear magnetic resonance (NMR)

A

spectroscopy

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2
Q

measures absorption of ____ light, which causes molecular vibration (can be seen as bond stretching, bending, twisting, and folding)

A

infrared (IR) spectroscopy

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3
Q

infrared (IR) spectroscopy:

general plot of IR spectrum

A

percent transmittance vs wavenumber (1/λ)

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4
Q

infrared (IR) spectroscopy:

normal range of IR spectrum

A

4000 to 400 cm^-1

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5
Q

infrared (IR) spectroscopy:

between 1500 and 400 cm^-1; contains a number of peaks that can be used to identify a compound

A

fingerprint region

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6
Q

infrared (IR) spectroscopy:

must be changed by the vibration of a bond to appear on an IR spectrum

A

bond dipole moment

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7
Q

infrared (IR) spectroscopy:
have characteristic absorption frequencies, which allow us to infer the presence (or absence) of particular functional groups

A

specific bonds

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8
Q

infrared (IR) spectroscopy:

a broad peak around 3300 cm^-1

A

O-H peak

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9
Q

infrared (IR) spectroscopy:

a sharp peak around 3300 cm^-1

A

N-H peak

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10
Q

infrared (IR) spectroscopy:

a sharp peak around 1750 cm^-1

A

C=O peak

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11
Q

measures absorption of ____ light, which causes movement of electrons between molecular orbitals

A

ultraviolet (UV) spectroscopy

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12
Q

ultraviolet (UV) spectroscopy:

general plot of UV spectrum

A

percent transmittance or absorbance vs wavelength

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13
Q

ultraviolet (UV) spectroscopy:

must be small enough to permit an electron to move from one orbital to the other to appear on a UV spectrum

A

energy difference between HOMO and LUMO

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14
Q

ultraviolet (UV) spectroscopy:

shifts the absorption spectrum to higher maximum wavelengths (lower frequencies)

A

conjugation

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15
Q

measures alignment of nuclear spin with an applied magnetic field, which depends on the magnetic environment of the nucleus itself; useful for determining the structure (connectivity) of a compound, including functional groups

A

nuclear magnetic resonance (NMR) spectroscopy

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16
Q

nuclear magnetic resonance (NMR) spectroscopy:

push the nucleus from the α-state to the β-state, and these frequencies can be measured

A

radiofrequency pulses

17
Q

nuclear magnetic resonance (NMR) spectroscopy:

low-energy state

A

α-state

18
Q

nuclear magnetic resonance (NMR) spectroscopy:

high-energy state

A

β-state

19
Q

nuclear magnetic resonance (NMR) spectroscopy:

a medical application of NMR spectroscopy

A

magnetic resonance imaging (MRI)

20
Q

nuclear magnetic resonance (NMR) spectroscopy:

general plot of NMR spectrum

A

frequency vs absorption of energy

21
Q

nuclear magnetic resonance (NMR) spectroscopy:

standardizes plot of NMR spectra, measured in parts per million (ppm) of spectophotometer frequency

A

chemical shift (δ)

22
Q

nuclear magnetic resonance (NMR) spectroscopy:

used to calibrate NMR, has a chemical shift of 0 ppm

A

tetramethylsilane (TMS)

23
Q

nuclear magnetic resonance (NMR) spectroscopy:

to the left in a NMR spectrum, where higher chemical shifts are found

A

downfield

24
Q

nuclear magnetic resonance (NMR) spectroscopy:

to the right on a NMR spectrum, where lower chemical shifts are found

A

upfield

25
Q

nuclear magnetic resonance (NMR) spectroscopy:

the most common type of NMR; each unique group of protons (-H) have their own peak

A

proton (^1H) NMR

26
Q

proton (^1H) NMR:

area under the curve of a peak, is proportional to the number of protons represented by the peak

A

integration

27
Q

proton (^1H) NMR:
occurs to protons when electron-withdrawing groups pull electron density away from the nucleus, allowing it to be more easily affected by the magnetic field; moves a peak further downfield

A

deshiedling

28
Q

proton (^1H) NMR:
caused when hydrogens are on adjacent atoms and they interfere with each other’s magnetic environment; a proton’s (or group of proton’s) peak is ____ into n+1 subpeaks, where n is the number of protons that are three bonds away from the proton of interest

A

splitting (spin-spin coupling)

29
Q

proton (^1H) NMR:

include doublets, triplets, and multiplets

A

splitting patterns

30
Q

proton (^1H) NMR:

shift from 0 to 3 ppm

A

alkyl groups

31
Q

proton (^1H) NMR:

shift from 2 to 3 ppm

A

alkynes

32
Q

proton (^1H) NMR:

shift from 4.6 to 6 ppm

A

alkenes

33
Q

proton (^1H) NMR:

shift from 6 to 8.5 ppm

A

aromatics

34
Q

proton (^1H) NMR:

shift from 9 to 10 ppm

A

aldehydes

35
Q

proton (^1H) NMR:

shift from 10.5 to 12 ppm

A

carboxylic acids

MCAT Organic Chemistry (12 decks)

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