organic analysis Flashcards
test tube reaction to identify: alcohols
add sodium solid
alcohol + sodium -> sodium ethoxide and hydrogen
test for hydrogen gas with squeaky pop test. put burning splint near mouth of test tube. oxygen in air and hydrogen will react to form a pop
dispose of excess sodium with excess alcohol
test tube reaction to identify: aldehydes, fehlings
add fehlings a and fehlings b in equal amounts. mix. and anti bumping granules
add wool on top to minimise fumes
warm gently in hot water bath
allow to stand
fehlings solution oxidises aldehydes,
forming c acid which dissociates yo form a carboxylate ion
test tube reaction to identify: aldehydes, tollens
prepare tollens by adding silver nitrate and sodium hydroxide
AgNO3+ NaOH -> AgOH + NaHO3
then 2AgOH -> Ag2O + H2O
then add aw ammonia
Ag2O + H2O + 4NH3 -> 2Ag(NH3)2.+ + 2OH-
tollens reagent will oxidise aldehyde into c acid. as it does this silver ions in tollens reagent are reduced to silver atoms forming precipitate of silver on the inside of the test tube
test tube reaction to identify: alkenes
add bromine water which is brown and shake vigorously. C=C will be attacked by Br2 electrophiles by electrophilic addition forming bromo alkanes
brown to colourless
test tube reaction to identify: c acid
add a carbonate eg NaHCO3. acid plus carbonate goes to salt plus carbon dioxide plus water
need a set up of two tubes to collect gas formed. delivery tube between them with bungs in both. reaction in one, gas produced will go into other. the other tube should have Ca(OH)2, limewater, in it.
limewater goes cloudy when CO2 because forms CaCO3, precipitate
test tube reaction to identify: h alkanes
add NaOH which will act as a nucleophile and form alcohols and halide ions
then becomes test for halide ions:
add nitric acid to neutralise other ions that could form positive results
add silver nitrate. will dissociate, silver ions react with halide ions to form solid silver halides. Cl, Br, I; white, cream, yellow
if need more: add dilute ammonia, will redissolve AgCl. add conc ammonia, will redissolve AgBr
use of mass spectrometry
find the molecular mass of a compound by determining it’s mass to charge ratio. sample is usually 1+ charge because of electrospray or electron impact. so yeah
used to find abundance of isotopes and consequently the average molecular mass
(if 2+ then the m/z will be half actual mass // if electrospray then mass is m/z - 1 because that 1 represents the H ion added)
what’s high resolution mass spec
an analytical technique which allows for more precise measurements of the ions mass
In MS the sample is vaporized, ionized, and accelerated towards a negatively charged plate where a current is induced portion or to an ions abundance
in high resolution must spectrometry the mass analyzer is able to separate ions with very similar m/z ratio, measuring it to several decimal places therefore providing exact masses
the use of hrms
measure Mr to many dp
compare mass to mass of constituent elements to find molecular formula
give a more sensitive form of mass spec
what’s infrared spectroscopy
an analytical technique using infrared radiation to determine the function of groups in an organic compound
how does it spectroscopy work
when infrared radiation is passed through a compound it will absorb the light at the frequencies at which its bonds vibrate. bonds in a molecule absorb infrared at characteristic wave numbers. different bonds absorb the radiation in different amounts. these varying amounts of absorbance / transmittance or measured + recorded on a spectrum allowing certain bonds and therefore functional groups to be identified
characteristic curve for oh alcohol at it’s wavenumber range
smooth wide dip in wavenumber range
characteristic curve for oh acid at it’s wavenumber range
rougher wide dip
both oh bonds are examples of what kind of absorption
broad
characteristic curve for c=c at it’s wavenumber range
narrow sharp curve
