Organic analysis-organic chemistry Flashcards
(14 cards)
Why are functional group reactions important in organic chemistry?
They allow identification and classification of organic compounds based on their reactivity and specific chemical behaviour.
How can alcohols be identified through chemical reactions?
React with sodium metal → effervescence due to H₂ gas
Oxidation with acidified potassium dichromate(VI):
Primary alcohol → aldehyde → carboxylic acid
Secondary alcohol → ketone
Tertiary alcohol → no reaction
Orange to green colour change confirms oxidation.
How can you distinguish between an aldehyde and a ketone?
Fehling’s solution:
Aldehyde → red precipitate
Ketone → no change
Tollens’ reagent:
Aldehyde → silver mirror
Ketone → no reaction
What is a simple test for a carboxylic acid functional group?
Add sodium carbonate or sodium hydrogencarbonate
Effervescence due to CO₂ gas confirms the presence of a –COOH group
How can alkenes be identified using a chemical test?
Add bromine water
If a C=C bond is present, orange colour decolourises
What is the main use of mass spectrometry in organic chemistry?
To determine the molecular formula of a compound using its molecular ion peak (M⁺).
What does the molecular ion (M⁺) peak in a mass spectrum represent?
The peak with the highest m/z value (excluding small isotope peaks) represents the relative molecular mass (Mr) of the compound.
How does high-resolution mass spectrometry improve accuracy in determining molecular formula?
It uses precise atomic masses (e.g. C = 12.0000, H = 1.0078, O = 15.9949) to calculate the exact molecular mass of a compound, helping distinguish between compounds with similar Mr.
How do you determine the molecular formula from a molecular ion peak?
Use the exact Mr from the M⁺ peak, compare with combinations of exact atomic masses, and find the formula that matches the total.
What causes a bond in a molecule to absorb infrared radiation?
When the frequency of IR radiation matches the natural frequency of vibration of a bond, it absorbs energy and vibrates more.
How can infrared spectra be used to identify functional groups?
By comparing absorption peaks (wavenumbers in cm⁻¹) to known values for specific bonds using the Data Booklet (e.g., C=O around 1700 cm⁻¹, O–H around 3200–3600 cm⁻¹).
What is the fingerprint region in an IR spectrum?
The region below 1500 cm⁻¹, unique for every compound, used for identifying molecules by comparison with spectra of known substances.
How can IR spectroscopy detect impurities in a compound?
Extra peaks in the spectrum (especially outside the fingerprint region) may indicate other functional groups not expected in the pure compound.
How is infrared absorption linked to global warming?
Greenhouse gases like CO₂, CH₄, and H₂O absorb IR radiation emitted from the Earth’s surface, trapping heat and contributing to the greenhouse effect.
