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Chemistry > Chapter 11- Measurement and Data Processing > Flashcards

Chapter 11- Measurement and Data Processing Flashcards

1
Q

IHD (Index of Hydrogen Deficiency)

A

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.

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2
Q

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

A

The number of rings or multiple bonds (π bond)

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3
Q

What is the IHD number of a:

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

A

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

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4
Q

Spectroscopy

A

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

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5
Q

c (velocity of wave)=?

A

vλ
→ v = freq.
→ λ = wavelength

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6
Q

E (Energy of electromagnetic radiation) =?

A

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

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7
Q

Radiowaves: what the energy does + Spectroscopy technique

A

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

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8
Q

Microwaves: what the energy does + Spectroscopy technique

A

+ Rotates molecules

+ Gives info. on bond length

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9
Q

Infrared: what the energy does + Spectroscopy technique

A

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

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10
Q

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

A

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

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11
Q

X-rays: what the energy does + Spectroscopy technique

A

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

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12
Q

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

A

Initiates reactions by ionising atoms and breakig chemical bonds

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13
Q

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

A

Excite a molecule to a higher vibrational level

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14
Q

What graph does IR-spec produce?

A

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

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15
Q

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

A

The presence of bonds in a molecule

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16
Q

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

A

Strength of the bond and masses of the atom

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17
Q

Light atoms vibrate at a?

A

Higher freq. than heavier atoms

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18
Q

Multiple bonds vibrate at a?

A

Higher freq. than single bonds

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19
Q

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

A

Stretching and bending

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20
Q

Only what kinds of molecules will absorb IR radiation?

A

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)

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21
Q

IR-spectroscopy: Symmetrical stretching mode

A

In molecules w/ dipole moment of 0

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

22
Q

IR-spectroscopy: Asymmetrical stretching mode

A

Stretching and bending modes of CO2 = BOTH absorb IR

23
Q

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

A

Broadening of absorption

24
Q

IR-spectroscopy: Fingerprint region

A

from 400-1500 cm^-1

→ unique to the compound

25
Q

Mass spectrometry can be used to determine what?

A

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

26
Q

Mass spectrometry: How does it work?

A

+ 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

27
Q

Mass spectrum records what?

A

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

28
Q

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

A

Because inside the spectrometer it is v. LOW pressure

29
Q

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

A

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

30
Q

Mass spectrometry: MOLECULAR ION is when?

A

+ A whole molecule is ionised M+

+ Whole molecule - 1 electron = MOLAR MASS

31
Q

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

A

+ Cuz C contains abt. 1% C13

→ so theirs always that smaller peak greater than the molecular ion peak

32
Q

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

A

+ Cause the molecules to breakdown into “Fragments”

→ gives rise to “Fragmentation patterns”

33
Q

Mass spectrometry: What do Fragmentation patterns give clues to?

A

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

34
Q

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

A

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!

35
Q

What are 2 uses of the Mass Spectra?

A

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

36
Q

HNMR and how works?

A

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.

37
Q

What does the NMR indicate?

A

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

38
Q

Chemical shift

A

The position of absorption/ppm

39
Q

Internal standard for HNMR, and why needed?

A

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”

40
Q

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

A

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

41
Q

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

A

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

42
Q

What is the HNMR showed in?

A

Integration Trace

43
Q

The more electronegative the chem environment?

A

The greater the chem shift

44
Q

What are splitting patterns caused by?

A

+ 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

45
Q

of peaks = ?

A

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

46
Q

Name of the peaks

A

+ Singlet
+ Doublet
+ Triplet
+ Quartet

47
Q

HNMR in body scans (MRI)

A

+ 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.

48
Q

What is X-Ray Crystallography used to identify?

A

Bond lengths and bond angles of crystalline compounds

49
Q

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

A

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

50
Q

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

A

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

51
Q

What does the diffraction pattern depend on? (3)

A

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

Chemistry (10 decks)

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