Analysis and Spectra

Question 1

deshielding

Answer 1

downfield (to the left) the nucleus will feel a stronger magnetic field.

chemical shift will increase because we’ve removed electron density

Question 2

shielding

Answer 2

upfield (to the right) -> high electron density

hydrophobic residues want to increase electronegative density and shield themselves from electronegative oxygen in water

electronegative atoms draw electron density from nearby protons

Question 3

Tollens test

Answer 3

used to identify presence of aldehydes and hydroxy ketones, including reducing sugars which have a free anomeric carbon

uses Ag(NH3)2+ to oxidize aldehydes to carboxylic acids

positive test –> formation of metallic silver deposited on glassware

Question 4

standard

Answer 4

used to optimize conditions for a purification and to predict the retention time of a known compound

Question 5

IR Spectroscopy

Answer 5

technique used to identify functional groups in a compound by analyzing the types of bonds present

sample shined with infrared light, which interacts with bonds
light absorbed in recorded and displayed as percent transmitted (y axis) vs wavenumber (x axis)

measures absorbance at different frequencies

shows bonds and functional groups present in a compound

Question 6

absorbance and transmittance

Answer 6

are directly inverse

100% absorption means 0% transmission

Question 7

wavelength equation

Answer 7

wavelength = speed of light/frequency

Question 8

wavenumber

Answer 8

inversely related to wavelength

directly related to frequency

Question 9

what does IR radiation measure

Answer 9

causes bond stretching, vibrations and rotations at different frequencies

Question 10

Do functional groups absorb the same amount or different amounts of energy?

Answer 10

different amounts depending on type of bond present

Question 11

What is found in the fingerprint region?

Answer 11

C-C
C-O
C-N

found between 600-1400

Question 12

Where are double bonds found in IR absorption range?

Answer 12

1600-1800

C =C
C=O
C=N

Question 13

Where are triple bonds found in the IR absorption range?

Answer 13

C triple bond N
C triple bond C

2100-2400

Question 14

Where are the single bonds found in the IR absorption range?

Answer 14

N-H
O-H
C-H

2700-3500

Question 15

thin layer chromatography

Answer 15

separates compounds based on polarity

cells migrate up a plate and can be visualized with the absorption of UV light

UV light carries a large amount of energy that can excite the electrons of UV chromphores to higher energy states

Question 16

UV chromophores

Answer 16

bond types that can absorb UV light

double bonds, triple bonds, carbonyls, nitroso (R-N=O), alkyl halides (X-R), and conjugated systems

Question 17

H-NMR spectroscopy

Answer 17

uses radio waves to detect hydrogen atoms and excite them from the alpha spin to the beta spin state

Question 18

mass spectrometry

Answer 18

separate based on charge. the more massive molecules curve less on the machine. Sample is ionized by high-energy electrons, but the electrons do not change energy levels

measures the size of one molecules
looks at mass to charge ratio

Question 19

Normal Phase Thin Layer Chromatography

Answer 19

mobile phase = non-polar (organic solvent)
stationary phase = polar (silica)

non-polar compounds have less affinity for the polar stationary phase so will travel further up the plate

Question 20

TLC Rf value

Answer 20

distance compound traveled from origin/distance from origin to solvent front (very top of plate)