Chapter #11

Question 1

what does spectroscopy do?

Answer 1

spectroscope measures the energy differences between the possible state of a molecular system by determining the frequencies of electromagnetic radiation absorbed by the molecules.

Question 2

what are some pros and cons to spectroscopy?

Answer 2

pros: only a small sample is needed and the sample can be reused after a test is performed
cons: it is difficult to do without special equipment.

Question 3

what does infrared (IR) spectroscopy measure?

Answer 3

molecular vibrations

can be seen as bond stretching, bending, or combinations of different vibrational methods.

Question 4

how is an IR spectrum recorded?

Answer 4

infrared light is passed through a sample and the absorbance is measured

Question 5

what is IR spec used for?

Answer 5

functional groups in the molecule, determines what bonds exist.

Question 6

what are the different types of vibration that occur in IR spec?

Answer 6

symmetric bend, asymmetric bend, symmetric stretch, asymmetric stretch

Question 7

what analog of frequency does IR spec use?

Answer 7

wavenumber

Question 8

wavenumber = 1/?

Answer 8

wavelength

Question 9

fingerprint region

Answer 9

more complex vibration patterns cause by motion of the molecule as a whole and are characteristic of each individual molecule

Question 10

what is require for an absorption to be recorded in IR spec?

Answer 10

the vibration must result in a change in the bind dipole moment

Question 11

what type of bonds do not show up on IR spec?

Answer 11

symmetric bonds in which there is no change in dipole moment.
ex: C2H2 and O2
ones that do: HCl or CO

Question 12

what is the IR spec peak for OH for alcohol

Answer 12

3300 cm^-1 broad

Question 13

what is the IR spec peak for OH for carboxylic acid

Answer 13

3000 cm^-1 broad

Question 14

compare IR spec peak for OH functional group for alcohol and carboxylic acid

Answer 14

carboxylic acid is less because the carbonyl pulls some of the electron density out of the O-H bond which shifts the absorption to a lower wavenumber (lower wavenumber is higher wavelength is lower frequency)

Question 15

what is the IR spec peak for carbonyl

Answer 15

1700 cm^-1 sharp

Question 16

what is the IR spec peak for N-H

Answer 16

3300 cm^-1 sharp

Question 17

what are the units for the graph of IR spec?

Answer 17

% transmittance vs. wavenumber

Question 18

what is % transmittance

Answer 18

the amount of light that passes through the sample and reaches the detector.

Question 19

for IR spec, max absorptions appear as what on the graph?

Answer 19

bottom (valleys)

Question 20

on IR graphs, wavenumber increases to the ___

Answer 20

left

Question 21

equation for absorbance

Answer 21

A = 2 - log (%T)

Question 22

what does ultraviolet (UV) spectroscopy measure?

Answer 22

absorbance of UV light

Question 23

what causes the absorbance of UV light?

Answer 23

electronic transitions between orbitals

Question 24

what is the electromagnetic spectrum

Answer 24

Gamma rays, x rays, UV rays, visible light, IR rays, microwaves, radiowaves

Question 25

what is the main thing the UV spectrum tells us?

Answer 25

tells us the wavelength of maximum absorbance which tells us the extent of conjugation within conjugated systems. used for measuring double bonds or heteroatoms with lone pairs that create conjugated systems.

Question 26

IR spectroscopy: the more conjugated the compound, the ____ the energy of the transition and the ____ the wavelength of maximum absorbance

Answer 26

lower | greater

Question 27

why does UV spec work?

Answer 27

nonbonding or pi electrons can be excited to higher energy antibonding orbitals

Question 28

____ energy gap between the HOMO and LUMO means absorbing longer wavelength absorbance (UV spec)

Answer 28

lower

Question 29

What is HOMO

Answer 29

highest occupied molecular orbital

Question 30

what is LUMO

Answer 30

lowest unoccupied molecular orbital

Question 31

UV spec: conjugation results in ___ maximum wavelengths

Answer 31

higher | lower frequencies

Question 32

what is NMR based on?

Answer 32

the fact that certain atomic nuclei have magnetic moment that are oriented at random but when they are placed in a magnetic field then their magnetic moments tend to align either with or against the direction of this applied field.

Question 33

NMR: nuclei with magnetic moments that are aligned with the field are said to be in the ____ state, a ___ energy state

Answer 33

alpha state | lower

Question 34

In NMR, the higher energy state is the ___ state

Answer 34

Beta

Question 35

NMR: chemical shift increases to the ____

Answer 35

left

Question 36

Further left on NMR is referred to as ____ field

Answer 36

down

Question 37

In NMR, the calibration standard is done with ___ and is at ___ ppm

Answer 37

TMS | 0 ppm

Question 38

nuclei with odd ___ or ____ will have magnetic moment when placed in a magnetic field

Answer 38

atomic number or mass number (or BOTH)

Question 39

In NMR, if multiple protons are _____ then they have the same magnetic environment and will have the same peak

Answer 39

chemically equivalent

Question 40

deshielding leads to a shift ____ field

Answer 40

down

Question 41

the height of the peak in NRM is proportional to ______

Answer 41

the number of protons it contains

Question 42

deshielding occurs when ______

Answer 42

electron density is pulled away The more the proton's electron density is pulled away, the less it can shield itself from the applied magnetic field, resulting in a reading further downfield.

Question 43

when does spin spin coupling occur?

Answer 43

when there are protons on adjacent carbons

Question 44

the magnitude of splitting is measured in ___ and is known as the ___

Answer 44

hertz | coupling constant

Question 45

n+1 rule

Answer 45

to determine the number of peaks present where n protons are bonded to the adjacent carbon.

Question 46

how do you work with protons attached to oxygen or nitrogen and splitting?

Answer 46

they are not split and do not contribute to splitting

Question 47

Splitting: number of adjacent hydrogens, total number of peaks, and area ratios:

Answer 47

``` 0 - 1 - 1 1 - 2 - 1:1 2 - 3 - 1:2:1 3 - 4 - 1:3:3:1 4 - 5 - 1:4:6:4:1 ```

Question 48

what are the general peaks for the following hydrogens: alkyl, alkyne, alkene, aromatic, aldehyde, and carboxylic acid?

Answer 48

alkyl: 0-3 alkyne: 2-3 alkene: 4.5-6 aromatic: 6-8.5 aldehyde: 9-10 carboxylic acid: 10.5-12

Question 49

what does NMR measure

Answer 49

it measures the alignment of the spin of a nucleus with the applied magnetic field.

Question 50

what is spin spin coupling?

Answer 50

occurs when two protons close to one another have an effect on the other's magnetic environment.

Question 51

what is the wavenumber for the fingerprint region?

Answer 51

1500 to 400 cm^-1

Question 52

what pushes the nuclei from their alpha to beta states

Answer 52

radiofrequency pulses | can be measured.

Question 53

where is NMR applied in medicine?

Answer 53

MRI

Question 54

Isotopes with non-odd atomic number or mass numbers have ____ and will_____

Answer 54

have no magnetic moment and will not exhibit resonance

Question 55

when is an electron excited form the HOMO to the LUMO

Answer 55

only after absorbing UV light

Question 56

In IR, higher order bonds have _____

Answer 56

higher order absorption frequencies