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AL. OCR Chemistry > spectroscopy > Flashcards

spectroscopy Flashcards

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1
Q

molecular ion peak

A

peak on spectrum formed when molecule looses an electron forming a positive ion and an electron
- on far right of spectrum (small M+1 peak after it)

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2
Q

what does molecular ion peak tell us?

A

the Mr of the compound

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3
Q

fragment ions

A

when molecular ion is broken down through fragmentation producing fragment ion + RADICAL

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4
Q

products of fragmentation

A

positive ion

uncharged radical - UNDETECTED

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5
Q

how does IR spectroscopy work?

A
  • atoms are joined by covalent bonds which contain energy and vibrate (increase as temp increase)
  • bond absorbs radiation at same frequency as bond
  • increases its vibrations
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6
Q

2 types of movement by covalent bonds

A

stretch

bend

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7
Q

how does global warming link to IR radiation

A
  • most of suns radiation doesn’t disturb atmospheric gases
  • some radiation re-emitted from earth and is longer wavelength IR radiation
  • absorbed in bonds In CO2, water vapour and methane
  • causing bonds to vibrate more and re-emit this energy as radiation which increases atmospheric temp close to the earths surface = global warming
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8
Q

fingerprint region

A

below 1500cm-1

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9
Q

use of fingerprint region

A

identify specific molecules as region is unique to each compound

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10
Q

O-H (alcohol) wavenumber

A

3200-3600

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11
Q

C-H wavenumber

A

2850-3100

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12
Q

C=O wavenumber

A

1630-1820

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13
Q

O-H (carb. acid) wavenumber

A

2500-3300 broad

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14
Q

applications of IR spectroscopy

A
  • pollutants can be identified using IR fingerprint region - remote sensors used to analyse IR spectra of vehicle emissions to monitor local pollution
  • breathalysers - pass beam of IR radiation through breath to detect ethanol
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15
Q

order of use of analysis for unknown compound

A

1) elemental - find empirical formula
2) mass spec - find molecular mass from molecular ion peak - fragment ions identify different sections of molecule
3) IR spec. - identify bonds and functional groups

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16
Q

what does NMR use (2)

A
  • magnetic frequency

- radio frequency radiation

17
Q

how does NMR work

A

(odd number) of nuclei spin -
has 2 different spin states, in right conditions (high frequency radiation and strong magnetic field) nucleus rapidly flips between 2 states = RESONANCE

18
Q

typical NMR radiowave frequencies

A

100, 200 or 400 MHz

19
Q

chemical shift

- units

A

difference in radio frequencies absorbed by nuclei in molecule being analysed and same nuclei in TMS
- ppm

20
Q

why deuteriated solvents?

A

doesn’t contain H1 - therefore won’t have signal on spectrum for NMR

21
Q

typical deuterated solvent

A

CDCl3

22
Q

what does C13 NMR tell us (2)

- from what?

A
  • number of C environments (number of peaks)

- types of C environments (chemical shift)

23
Q

what does proton NMR tell us (4)

- from what?

A
  • number of H environments (number of peaks)
  • type of environment (chemical shifts)
  • relative number of H in each environment (relative area of signals)
  • number of Hs on adjacent carbons (splitting patterns)
24
Q

what causes splitting?

- what does it tell us?

A

H atoms on adjacent carbons

N+1 rule

25
Q

uses of chromatography

A

analysis of:

  • drugs
  • plastics
  • flavourings
  • air samples
26
Q

chromatography has 2 things:

A

1) stationary phase - doesn’t move, usually solid or liquid in solid
2) mobile phase - does move - gas or liquid

27
Q

adsorption (TLC)

A

process by which silica hold different substances in the mixture to its surface

28
Q

how does TLC work?

A
  • TLC plate coated in solid absorbant substance (silica) = stationary phase
  • different components of sample have different affinities for absorbent and bind to its surface with different strengths
29
Q

TLC method

A
  • draw line across bottom of TLC plate 1cm from bottom = base line
  • use capillary tube to spot a small amount of solution of sample onto base line
  • prepare solvent in beaker - 0.5cm depth
  • suspend TLC plate in solvent - place bath glass over to avoid evaporation
  • when solvent is 1cm form top of plate remove plate and mark solvent front
  • circle any defined dots
    leave to dry
  • calculate Rf
30
Q

purpose of gas chromatography

A

separating and identifying volatile compounds in organic mix.

31
Q

stationary phase in gas chromatography

A

high boiling liquid absorbed onto inert solid support

32
Q

mobile phase in gas chromatography

A

inert carrier gas - eg. neon/helium

33
Q

how does gas chromatography work?

A
  • small amount of mix is injected into apparatus - mobile phase carriers components through capillary column which contains stationary phase
  • components slow as they enter stationary phase - more soluble component is the slower it moves
  • compounds reach detector at different times depending on solubility in stationary phase - lowest retention time detected first
34
Q

retention time

A

time taken for each component to travel through column

35
Q

what does gas chromatography tell us

A
  • identify components - from retention time

- concentration of components - through peak integrations (area under peak)

36
Q

how to find concentrations form gas chromatography

A
  • prepare standard solutions of known concs of compound being investigated
  • get chromatograms for each
  • plot calibration curve of peak area vs. conc. = EXTERNAL CALIBRATION
  • obtain gas chromatogram for component under investigation
  • use calibration curve to find conc.
37
Q

what does external calibration do

A

converts peak area into conc.

38
Q

why may peaks in NMR spec. be outside of ranges of values?

A

factors eg. conc, solvents move them

AL. OCR Chemistry (20 decks)

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