Organic analysis Flashcards
What is the reagent and positive test result for primary and secondary alcohols
Reagent: acidified pottasium dichromate (K₂Cr₂O₇)
Primary and secondary alcohols are oxidised by K₂Cr₂O₇.
Will turn from orange to green (Cr₂O₇²⁻ to Cr³⁺)
What is the reagent and positive test result for a tertiary alcohol
Will remain orange on addition of acidified potassium dichromate
What is the reagent and positive test result for alkenes
Reagent: Bromine water - goes from orange to colourless in the presence of an alkene
What is the reagent and positive test result for an aldehyde
Reagent: Fehling’s solution (in hot water bath) - goes from a blue solution to a red precipitate in the presence of an aldehyde
or
Reagent: Tollens reagent (in hot water bath)- formation of a silver mirror in the presence of an aldehyde
What is the reagent and positive test result for a carboxylic acid
Write an equation for the positive test with CH3CO2H
Reagent: Add sodium carbonate
Effervescence of CO2 formed - can then bubble through limewater to test this
2CH3CO2H + Na2CO3 —. 2CH3CO2Na + H2O + CO2
What is the reagent and positive test result for chloroalkanes
Reagent: Warm with silver nitrate
Slow formation of white precipitate AgCl
Write an equation for the reaction of CH3CHO with tollens. Write the practical steps to test it and what occurs
Tollens’ Reagent formed by mixing aqueous
ammonia and silver nitrate, which we heat gently in a water bath then add what were testing
Aldehydes are oxidised by tollens into a carboxylic acid, and silver ions are reduced to silver atoms (silver mirror)
CH3CHO + 2Ag+ + H2O —> CH3COOH + 2Ag + 2H+
Write an equation for the reaction of CH3CHO with Fehlings. Write the practical steps to test it and what occurs
We heat gently in a water bath then add what we are testing
Aldehydes are oxidised by Fehling’s Solution
into a carboxylic acid. The copper (II) ions are reduced
to copper(I) oxide (blue to brick red)
CH3CHO + 2Cu2+ + 2H2O —-> CH3COOH + Cu2O + 4H+
What is the m+1 or molecular ion peak
The peak with the highest mass/charge ratio which will be normally due to the original molecule that hasn’t fragmented, and therefore be equal to Mr
When is high resolution mass spectrometry useful
When identifying different molecules with he same Mr rounded to the nearest whole number
When does M+2 peak apply
If a compound contains a chlorine or a bromine atom then two molecular ion peaks will occur : a M and a M+2 peak will occur due to the two naturally occurring isotopes of chlorine or bromine.
What is the ratio of the 2 isotopes of Cl
Chlorine exists as Cl35 (75%) and Cl37 (25%)
Bromine exists as Br79 (50%) and Br81 (50%)
What is the ratio of the heights of the M and M+2 peak in CH3Cl
CH3Cl will have a m/z value of M of 50 (CH3Cl 35) and M+2 of 52 (CH3Cl 37)
The ratio of heights M:M+2 will be 3:1
What is the ratio of the heights of the M and M+2 peak in CH3Br
CH3Br will have m/z value of M of 94 (CH3Br 79) and M+2 of 96 (CH3Br 81) The ratio of heights M:M+2 will be 1:1
When will an M+4 peak occur
If a compound contains two chlorine or bromine atoms
What is the ratio of the heights of the M, M+2 and M+4 peak in C2H4Cl2
C2H4Cl2 will have a m/z value of M of 98 (C2H4Cl(35)Cl(35)) , a
M+2 of 100 (C2H4Cl(35)Cl(37)) and a M+4 of 102 (C2H4Cl(35)Cl(37))
The ratio of heights M:M+2: M+4 will be 9:6:1
What is the ratio of the heights of the M, M+2 and M+4 peak in C2H4Br2
C2H4Br2 will have a m/z value of M of 186 (C2H4Br(79)Br(79)) , a M+2 of 188 (C2H4Br(79)Br(81)) and a M+4 of 190 (C2H4Br(81)Br(81))
The ratio of heights M:M+2: M+4 will be 1:2:1
What is the ratio of the heights of the M, M+2 and M+4 peak in C2H3Cl3
C2H3Cl3 will have a m/z value of M of 132 (C2H4Cl(35)Cl(35)Cl (35)) , a M+2 of 134 (C2H4Cl(35)Cl(35)Cl(37) , a M+4 of 136 (C2H4Cl(35)Cl(37)Cl(37)) and a M+6 of 138 (C2H4Cl(37)Cl(37)Cl(37))
The ratio of heights M:M+2:M+4:M+6 will be 27:27:9:1
What does the frequency of infrared radiation absorbed by a covalent bond depend on
The atoms on either side of the bond
The position of the bond in the molecule
Where do we look to identify a functional group in infrared spectroscopy
Above 1500 cm-1
What does the fingerprint region in infrared spectrometry tell us
The size and position of the peaks are unique to a particular molecule, we can compare this region against a known library of spectra to identify a molecule
Where is the fingerprint region in infrared spectrometry
Between 500cm-1 and 1500cm-1
What do extra peaks in the fingerprint region of an infrared spectra indicate
Impurities in the sample
Explain how the greenhouse effect works
Electromagnetic radiation from the sun reaches the earth and is absorbed by land and sea. Some of this radiation is re-emitted as infrared
Covalent bonds in greenhouse gasses absorb this radiation and re-emit this back towards earth (which warms the earth up as it cant escape)
