Spectroscopy

Question 1

Absorption

Answer 1

Electron is excited to a high-energy orbital (HOMO to LUMO)

Question 2

Emission

Answer 2

Electron relaxes back to a lower-energy orbital (LUMO to HOMO)

Question 3

UV-Vis Spec is good to visualize _____?

Answer 3

Pi Electrons. Will promote an electron on a pi-bonding orbital to a pi antibonding orbital.

Question 4

Spectroscopy

Answer 4

The interaction between light and matter

Question 5

IR Spectroscopy induces _?

Answer 5

Symmetric and asymmetric stretching and bending of bonds

Question 6

What bond is seen at 2840-3000cm^-1?

Answer 6

saturated C-H on alkane

Question 7

What bond is seen at 3200-3650cm^-1

Answer 7

broad and rounded O-H stretch

Question 8

What bond is seen at 1630-1780 cm^-1

Answer 8

C=O stretch (narrow and pointed)

Question 9

On IR Spectrum, what does the x-axis and y-axis display?

Answer 9

X-axis - wavenumber
Y-axis - transmittance

Question 10

In HNMR looks at?

Answer 10

Chemical shift
Integration
Splitting Patterns

Question 11

What is the reference peak on NMR spetra?

Answer 11

Tetramethylsilane (TMS) at 0 ppm.

Question 12

What happens if a proton is close to an electronegative atom?

Answer 12

It will have its electron density withdrawn or deshielded. Peak will be futher downfield (to the left)

Question 13

Integration values

Answer 13

Relative to a reference peak
The higher the peak, the more chemically equivalent protons.

Question 14

When evaluating splitting patterns

Answer 14

Neighboring protons will create singlets, doublets, and so on. Each resonance is split into (n +1) peaks n = # of neighboring protons.

Question 15

Shifts for benzene rings in HNMR

Answer 15

Will be jumbled together usually seen between 7-8ppm.

Question 16

How do you calculate degrees of unsaturation in hydrocarbons?

Answer 16

(max #H atoms - actual # H atoms)/2
fully saturated hydrocarbons: CnH2n+2

Question 17

How to calculate the degrees of unsaturation in molecules with heteroatoms

Answer 17

DOF = (2C + 2 + N - X - H)/2

Question 18

Value for hydroxyl/amino protons in HNMR?

Answer 18

0.5-5.5ppm

Question 19

Value for sp3 C protons in HNMR?

Answer 19

1-5ppm

Question 20

Value for sp2 C protons in HNMR?

Answer 20

4-6ppm

Question 21

Value for aromatic protons in HNMR?

Answer 21

6-8ppm (identifies 4 DOF)

Question 22

Value for aldehyde/phenol protons in HNMR?

Answer 22

~10ppm

Question 23

Value for carboxyl/amide protons in HNMR?

Answer 23

12-14ppm

Question 24

Value for esters/amides/carboxylic acid carbons in 13CNMR?

Answer 24

160-180 ppm

Question 25

Value for aldehydes/ketone carbons in 13CNMR?

Answer 25

200-280ppm

Question 26

Value for sp3 alkane carbons in 13CNMR?

Answer 26

10-50ppm

Question 27

Value for sp2 alkene carbons in 13CNMR?

Answer 27

100-155ppm

Question 28

Value for aromatic carbons in 13CNMR?

Answer 28

120-180ppm

Question 29

Chromatography separates substances on the basis of differing:

Answer 29

Polarity

Question 30

The (blank) polar a substance, the more (blank) it will travel up a TLC plate.

Answer 30

More; Slowly

Question 31

Rf value must be between what values?

Answer 31

0;1

Question 32

Extraction separates liquids on the basis of differing:

Answer 32

Solubility

Question 33

Which substance would be most useful in separating benzoic acid and napththalene?

Answer 33

acqueous base like NaHCO3

Question 34

In Gas Chromatograhy, what factors cause a lower retention time?

Answer 34

Lower BP Lower solubility Hotter column

Question 35

Distillation separates liquids on a basis differing in:

Answer 35

Boiling points

Question 36

After recrystallization, melting point analysis can be performed. How do you know you have a pure substance based on melting values?

Answer 36

Narrow range clsoe to tabulated value.

Question 37

What kind of solvent is ideal for recrystallization?

Answer 37

Low solubility at room temperature and high solubility at high temperatures. Impurity should have high solubility at room temperature or insolubility at high temperature to remove while boiling

Question 38

What is Tollen's test?

Answer 38

Mainly used to test for aldehydes. In the reaction, silver ammonia complex ions react with aldehydes to form solid silver and carboxylate ions. The indicator of a positive result is a silver layer along the inside of the test tube.