Chapter 16 - Organic Analysis Flashcards

1
Q

how can you test for alkenes

A

add bromine water
brown to colourless when alkene present

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2
Q

how can you test for tertiary alcohols

A

add acidified potassium dichromate
if nothing happens (remains orange) then tertiary alcohol present

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3
Q

why does acidified potassium dichromate remain orange when a tertiary alcohol is added

A

because acidified potassium dichromate is an oxidizing agent, and tertiary alcohols cannot be oxidised.

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4
Q

how can you distinguish between primary and secondary alcohols

A

add tollens reagent
silver mirror forms for aldehydes
or
add Fehling’s solution
brick red precipitate forms if aldehyde present

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5
Q

how can you test for a carboxylic acid

A

add sodium carbonate
effervescence means acid is present

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6
Q

what is low resolution mass spectrometry useful for and why

A

for testing between samples of different substances
because it isnt as expensive as high res spectrometry and still gives accurate results to 1dp

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7
Q

what is high resolution mass spectrometry useful for and why

A

for testing between samples of substances with different molecular formulae but same MR
it gives the precise m/z ratio to 5dp

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8
Q

why are fragment peaks often bigger than the actual sample peaks

A

because fragmentation of molecules occurs very often leading to a greater ratio of fragments to whole molecules

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9
Q

what leads to fragmentation

A

when energetically unstable molecular ions dissociate

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10
Q

what is a molecular ion

A

a molecule with a single positive charge

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11
Q

how can mass spectra with fragmentation be useful

A

analysis can provide useful information about the structure of the molecule

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12
Q

how can you determine the m/z ratio of the whole molecule form a fragmentation spectrum

A

the highest m/z ratio is of the whole unfragmented molecule, not highest peak

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13
Q

whats the mr of a CH3+ fragment

A

15

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14
Q

whats the mr of a O+ fragment

A

16

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15
Q

whats the mr of a OH+ fragment

A

17

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16
Q

whats the mr of a CN+ fragment

17
Q

whats the mr of a C2H3+ fragment

18
Q

whats the mr of a C2H4+ or CO+ fragment

19
Q

whats the mr of a C2H5+ or CHO+ fragment

20
Q

whats the mr of a C3H7+ or C2H3O+ fragment

21
Q

whats the mr of a C4H9+ or C3H5O+ fragment

22
Q

whats the mr of a C5H11+ or C4H7O+ fragment

23
Q

why do molecules absorb some IR light

A

because when their bonds vibrate at the same frequency as the wave, they absorb it
this doesnt apply to molecules made of one element

24
Q

how does IR spectroscopy work

A

a beam of IR is passed through a sample cell (with the sample in it) and a reference cell (with nothing in it).
as the IR passes through the sample, some wavelengths of IR are absorbed by the bond’s vibrations so that the IR that comes out has lower transmittance for certain wavelengths
the exiting waves are detected, and spectrums are produces which have peaks for the wavelengths have been absorbed

25
Q

what is wavenumber

A

1/wavelength(in cm)

26
Q

what is the fingerprint region

A

the region in a IR absorbtion spectrum below 1500/cm

27
Q

how can you determine exactly which molecule is present using it IR spectrum

A

compare the fingerprint regions
when they are identical the molecules are the same

28
Q

why is the mr of carbon 12.00000

A

because carbon is used as a reference mr
it is 12.00000 by definition