Organic Analysis + NMR Flashcards
What is the test for alkenes and what is the observation
Bromine water
Orange colour decolourises
What is the test for Aldehydes and Ketones and what is the observation
Heat gently with both
Fehlings solution- Blue to red
Tollens reagent-Silver mirror forms
No change if ketone is present
(tollens is silver nitrate+NaOH)
What is the test for carboxylic acid and what is the observation
Sodium carbonate or sodium hydrogencarbonate
Effervesence
What is the test for alcohols and what is the observation
Warm with acidified pottasium dichromate k2Cr2O7
Orange to green
(oxidises primary and secondary)
(tertiary cannot be oxidised)
What is the test for haloalkanes and what is the observation
- Acidified silver nitrate (AgNO3)aq –> colour change will be given
2.White-Chlorine, Cream-Bromine,Yellow-Iodine
3.To differentiate between white and cream you can test for chlorine by using dilute ammonia solution which dissolves the white
4.To differentiate between the cream and white you can use concentrated ammonia solution which dissolves the cream if bromine is present
What are you going to find if the wave number is above 1500 and below 1500 in infrared spectroscopy
Functional groups
Fingerprinting region-This part of the spectrum is unique for every compound, and so can be used as a “fingerprint”.
extra
“rogue” absorptions can also occur and are indicators of impurities
the fingerprint region also can be used to check if a sample is pure
Mechanism of greenhouse effect
*UV wavelength radiation passes through the atmosphere to the Earth’s surface and heats up Earth’s surface.
*The Earth radiates out infrared long wavelength radiation.
*The C=O Bonds in CO2
absorb infrared radiation so the IR radiation does not escape from the atmosphere.
*This energy is transferred to other molecules in the atmosphere by collisions so the atmosphere is warmed.
Absorbance of IR radiation
Bond polarity-Absoption of IR radiation is significantly stronger if there is a polar bond (Delta negative and delta positive)
Molecules can vibrate making them longer or shorter for example by stretching
How could you prove this was an IR spectrum for propanal (peak at 1680)
Compare the spetrum for our unknown substabce that is propanal to a data base of known spectra
IF there is an exact match it will be a sample of propanal
Define resolution (not the biological definition)
Ability to tell one thing apart from another
Why is High res mass spec needed
It allows you to tell apart certain compounds that have very similar Mr as it give the Ar of atoms to 5 dp
how could high res mass spec be used to prove that a sample of propane gas was contaminated with carbon dioxide
Find the Mr of both compounds with the Ar of the atoms being up to 5 dp
What is the purpose of the mass spec and IR radiation
IR radiation can be used to identify the functional group and some bonds whilst the mass spec can be used to identify the precise Mr
What are the charcteristics of IR peaks (6)
*N-H Smaller peak than OH(alcohol) but is sharper
*C=N (triple bonded)-Often narrow and sharp
*C=C-Narrow but relatively weak absorbption
*C=O-Narrow but very strong
*O-H-Acid-Very broad and overlapp with c-h
*O-H Alcohol-Very broad but not as broad as OH acid
How to distinguish between primary and secondary alcohols
Fractional distillation is used and test the product to see if an aldehyde or ketone forms
(aldehyde made from primary and ketone from secondary)
fingerprint
unique funger print
extra peaks reveal that it is impure
Rules of solvent
- Solvent must not interfere with the spectrum e.g.any protons in the solvent would create a peak and add to the spectrum for the sample
- must dissolve the sample
What sample dissolves the polar substance and non polar substance
A polar sample can only dissolve in a polar solvent e.g.CDCl3
similarly a non polar substnace must be dissolved ina non polar solvent e.g. CCl4 (tetrachloromethane)
What is Heavy hydrogen
Hydrogen with a nuetron known as deuterium (D)
What is tetramethyl silane and give features of it
Si with 4CH3’s bonded to it
Si(CH3)4
Only gives a single peak due to its enviornments
It will pick up a single peak at 0 on any scale
It is inert:Wont react with the sample
Non toxic;ANalysts less risk of harm
Volatile therefore eays to separate from the sample
Two triplets
suggest 2CH2’s
