Chapter 11- Measurement and Data Processing

Question 1

IHD (Index of Hydrogen Deficiency)

Answer 1

Is a measure of “How many molecules of H2” would be needed in ‘Theory’ to convert the molecule to the corresponding saturated, non-cyclic molecule.

Question 2

What can the IHD be used to determine in a molecule?

Answer 2

The number of rings or multiple bonds (π bond)

Question 3

What is the IHD number of a:

1) Double bond
2) Triple bond
3) Ring
4) Aromatic ring (Benzene)

Answer 3

1) 1 (1 degree of saturation)
2) 2 (2 degrees of saturation)
3) 1 (1 degree of saturation)
4) 4 (4 degrees of saturation)

Question 4

Spectroscopy

Answer 4

The way in which the absorption or emission of electromagnetic radiation by substance varies w/ frequency

Question 5

c (velocity of wave)=?

Answer 5

vλ
→ v = freq.
→ λ = wavelength

Question 6

E (Energy of electromagnetic radiation) =?

Answer 6

hv
→ h = Planck’s constant (6.626 x 10^-34 Js)
→ v = freq.

Question 7

Radiowaves: what the energy does + Spectroscopy technique

Answer 7

+ Reverse Nuclear spin on certain atoms when in a strong magnetic field
+ NMR- spectroscopy
→ gives info. abt the chemical environment of atoms (usually H)

Question 8

Microwaves: what the energy does + Spectroscopy technique

Answer 8

+ Rotates molecules

+ Gives info. on bond length

Question 9

Infrared: what the energy does + Spectroscopy technique

Answer 9

+ Vibrates (stretches and bends) bonds in molecule
+ IR-spectroscopy
→ info. on bonds present

Question 10

UV/Visible light: what the energy does + Spectroscopy technique

Answer 10

+ Cause electronic transitions in atoms and molecules
+ UV-vis-spectroscopy
→ info. abt electronic energy levels

Question 11

X-rays: what the energy does + Spectroscopy technique

Answer 11

+ Produce diffraction patterns as their λ is similar to inter-atomic distances.
+ X-ray crystallography
→ info. on bond lengths and angles

Question 12

What does too much exposure to the electromagnetic radiations do to make them harmful?

Answer 12

Initiates reactions by ionising atoms and breakig chemical bonds

Question 13

IR-spectroscopy: what does the infrared wave of light do?

Answer 13

Excite a molecule to a higher vibrational level

Question 14

What graph does IR-spec produce?

Answer 14

+ transmission against freq. (often expressed as wavenumber= 1/λ) when infrared is passed through the sample

Question 15

What does the absorption in a particular freq. range indicate?

Answer 15

The presence of bonds in a molecule

Question 16

Each bonds vibrate at a particular freq. depending on what?

Answer 16

Strength of the bond and masses of the atom

Question 17

Light atoms vibrate at a?

Answer 17

Higher freq. than heavier atoms

Question 18

Multiple bonds vibrate at a?

Answer 18

Higher freq. than single bonds

Question 19

What are the 2 types of vibration possible in IR-spec?

Answer 19

Stretching and bending

Question 20

Only what kinds of molecules will absorb IR radiation?

Answer 20

Vibrational molecules that result in a change of DIPOLE moment (polarity) of a molecule.
→ O=O and H-H = DON’T absorb IR = cuz non-polar even on stretching (dipole moment = 0)

Question 21

IR-spectroscopy: Symmetrical stretching mode

Answer 21

In molecules w/ dipole moment of 0

→ e.g CO2 = maintains symmetry and dipole moment = 0 therefore doesn’t absorb IR

Question 22

IR-spectroscopy: Asymmetrical stretching mode

Answer 22

Stretching and bending modes of CO2 = BOTH absorb IR

Question 23

IR-spectroscopy: What do presence of H.bonds cause to happen in the absorption?

Answer 23

Broadening of absorption

Question 24

IR-spectroscopy: Fingerprint region

Answer 24

from 400-1500 cm^-1

→ unique to the compound

Question 25

Mass spectrometry can be used to determine what?

Answer 25

The MOLAR MASS of a substance and give some info. on the structure of the molecule

Question 26

Mass spectrometry: How does it work?

Answer 26

+ Gaseous molecules = converted to + ions (cations) + which are ACCELERATED into an *Electric field* and DEFLECTED by *Magnetic field* → so they are separated according to their mass/charge (m/z) ratio

Question 27

Mass spectrum records what?

Answer 27

The of the fragments of diff. m/z ratio reaching the detector

Question 28

Mass spectrometry: Why are collisions betw/ particles = v. unlikely?

Answer 28

Because inside the spectrometer it is v. LOW pressure

Question 29

Mass spectrometry: What does the ion with the greatest mass usually correspond to?

Answer 29

A molecule that has only lost a → The *MOLECULAR ION* = gives the Relative Molecular Mass (Mr) of the substance

Question 30

Mass spectrometry: MOLECULAR ION is when?

Answer 30

+ A whole molecule is ionised M+ | + Whole molecule - 1 electron = MOLAR MASS

Question 31

Mass spectrometry: Why is there always a much smaller peak at 1 greater than the Molecular ion peak?

Answer 31

+ Cuz C contains abt. 1% C13 | → so theirs always that smaller peak greater than the molecular ion peak

Question 32

Mass spectrometry: What does the excess energy from the impact of the electron forming the Molecular ion cause?

Answer 32

+ Cause the molecules to breakdown into "Fragments" | → gives rise to "Fragmentation patterns"

Question 33

Mass spectrometry: What do Fragmentation patterns give clues to?

Answer 33

The structure of the molecule through the mass of the units that's broken off

Question 34

Mass spectrometry: What happens when only 1 H breaks off? (Fragmentation patterns)

Answer 34

It gives a peak at one mass # less than the main peak? | → cause the mass of H = 1 so the substance now weighs 1 less!

Question 35

What are 2 uses of the Mass Spectra?

Answer 35

1) Radiocarbon dating → used to detect the % of C14 present in samples 2) Forensic Science → Determine the presence of small amts of drugs and other substances

Question 36

HNMR and how works?

Answer 36

Hydrogen Nuclear Magnetic Resonance + Results from the changes that occur in the nucleus atoms w/ an odd mass # → when placed in magnetic field = absorbs radiation of radio freq.

Question 37

What does the NMR indicate?

Answer 37

Gives info abt. the chemical environment of the H atoms in the molecule

Question 38

Chemical shift

Answer 38

The position of absorption/ppm

Question 39

Internal standard for HNMR, and why needed?

Answer 39

TMS (Tetramethylesilane) → The freq. of radiation = dependent on the strength of the applied magnetic field = difficult to ensure that it'll remain constant + By adding TMS = can record the absorption relative to TMS = "arbitrary 0"

Question 40

Why is TMS used as an "internal standard"? (3)

Answer 40

1) Chemically inert 2) Produces a 'single' string signal (as it has 12 hydrogens in an identical environment) 3) Cuz of the low electronegativity of Silicon → It absorbs radiation of a freq. different from that of MOST other Organic compounds → DOESN'T INTERFERE W/ ABSORPTION SIGNALS

Question 41

The nuclei of the H atoms possess a spin what happens when the electric field applied?

Answer 41

The nuclei align themselves either: + with or against the field → The nuclei can absorb a photon of energy to move from the lower to the higher spin state

Question 42

What is the HNMR showed in?

Answer 42

Integration Trace

Question 43

The more electronegative the chem environment?

Answer 43

The greater the chem shift

Question 44

What are splitting patterns caused by?

Answer 44

+ When the precise freq. at which the absorption occurs = influenced by the direction of magnetic field of any hydrogens attached to the neighboring C atom of the one producing the signal

Question 45

of peaks = ?

Answer 45

The number of H on the neighboring C + 1 (n+1)

Question 46

Name of the peaks

Answer 46

+ Singlet + Doublet + Triplet + Quartet

Question 47

HNMR in body scans (MRI)

Answer 47

+ water and lipids are the main constituents of the body than contain H atoms + Water - lipid ration in parts of body = diff = absrob radio freq differently + Radio waves = harmless + Used to diagnose cancer, multiple sclerosis and other conditions.

Question 48

What is X-Ray Crystallography used to identify?

Answer 48

Bond lengths and bond angles of crystalline compounds

Question 49

Why can X-rays be used to determine the molecular and atomic structure of crystals?

Answer 49

Because the wavelength is similar to the dist. betw/ atoms

Question 50

What happens when an X-ray is passed through a crystalline solid?

Answer 50

They are scattered in an orderly way by their interactions w/ electrons in the substance → Diffraction patter produced

Question 51

What does the diffraction pattern depend on? (3)

Answer 51

+ angle of incidence of the X-ray (θ) + Wavelength of the incidence ray (λ) + dist. betw/ atoms (d)