Spectroscopy/Spectrometry

Question 1

What is spectroscopy?

Answer 1

interaction of rays or waves with molescules

Question 2

What types of spectroscopy are there?

Answer 2

• X-Ray diffraction
• UV/Vis Spectroscopy
• IR Spectroscopy
• NMR spectroscopy
• Mass spectroscopy

Question 3

What is a spectrum?

Answer 3

out come of the measurement

Question 4

How does X-ray diffraction work?

Answer 4

• crystal structures can be determined by allowing a sample of crystalline compound to difract X-rays
• resulting diffraction pattern allows determination of spatial arrangement of atoms in molecule

Question 5

What are limiations of X-ray diffraction?

Answer 5

need for crystals (no liquids, oils, etc)

Question 6

How can structures be determined via UV-Vis spectroscopy?

Answer 6

• graph of light absorbance vs. wavelength in the range of ultraviolet and visible light
• when white light passes through a coloured substance, a portion of wavelength is absorbed (expressing the complimentary colour)

Question 7

How can absorbance be calculated?

Answer 7

Absorbance = log (I₀ /I)

Question 8

What is Lambert - Beer Law

Answer 8

Question 9

What are chromophores?

Answer 9

light absorbing structural units

Question 10

What does conjugation lead to in absorbance of structures?

Answer 10

conjugation leads to smaller energy gaps between HOMO and LUMO

Question 11

What is bathochromic?

Answer 11

a shift of absorption to a longer wavelength

Question 12

What is hypsochromic

Answer 12

a shift in absorbtion to a shorter wavelength

Question 13

How do IR spectrums work?

Answer 13

• allows direct observation of functional groups through detection of stretching and bending of bonds (rather than atoms themselves)

Question 14

usually, when a molecule vibratesm all bonds stretch and relax in combination. Under what conditions do bonds stretch independently?

Answer 14

bonds are:

• much stronger or weaker than other nearby
• between atoms that are much heavier or lighter than neighbours

Question 15

Do stronger bonds vibrate faster or slower?

Answer 15

faster

Question 16

Do lighter atoms vibrate more or less?

Answer 16

vibrate more

Question 17

Does more virbation mean absorption of short or long wavelength (high or low frequency)?

Answer 17

more vibration means, absorption of short wavelenghts and higher frequency

Question 18

What bonds can be found in IR spectrum from 4,000 to 2500 cm^-1

Answer 18

bond to hydrogen

• O - H
• N - H
• C - H

Question 19

what bonds can be found in the between the 2500 to 2000 IR spectrum

Answer 19

Triple bonds

Question 20

What bonds can be found from 2000 to 1500 cm-1?

Answer 20

Double bonds

• C=O
• C=N
• C=C

Question 21

What bonds can be from 1500 and less cm-1?

Answer 21

single bonds

Question 22

What is mass spectrometry?

Answer 22

determination of molecular weight and elemental composition of molecule

Question 23

How does mass spectrometry work?

Answer 23

1. ionization of the sample (giving mono, di, … charged molecule ions or fragments)
2. separation of ions according to their mass / charged molecule ions or fragments
3. detection

Question 24

How is the mass spectrum plotted?

Answer 24

intensity of each ion versus its m/z ratio

Question 25

How is NMR measured?

Answer 25

• Normally in solution
• use of deutured solvents (otherwise big solvent peak)
• using continuous wave instrument (FT NMR instruments)

Question 26

What spins can nuclei have?

Answer 26

• integral spins (e.g. I = 1, 2, 3, …)
• fractional spins (eg. I = 1/2, 3/2, 5/2, …)
• no spin, I = 0 ( eg. C12, O16, S32, …)
  *

Question 27

What happens to isotopes that do not spin ( I = 0)?

Answer 27

do not interact with magnetic field (not detectable by NMR)