Organic Analysis and Spectroscopy

A set of vocabulary flashcards covering chemical tests for functional groups, mass spectrometry, and infrared spectroscopy based on the lecture notes.

Alkene Test

Shake the compound with bromine water; the observation of the orange colour disappearing indicates the presence of a $C=C$ bond.

Halogenoalkane Test

1. Add $NaOH(aq)$ and warm; 2. acidify with $HNO_3$; 3. add $AgNO_3(aq)$. A precipitate of $AgX$ identifies the halogen present.

Alcohol Test

Add acidified $K_2Cr_2O_7$; the orange colour turns green in the presence of primary or secondary alcohols.

Aldehyde Test (Fehling's)

Warm the compound with Fehling's solution; a change from a blue colour to a red precipitate indicates an aldehyde group ($R-CHO$).

Aldehyde Test (Tollens')

Warm the compound with Tollens' solution; the formation of a silver mirror indicates the presence of an aldehyde group ($R-CHO$).

Carboxylic Acid Test

Add $NaHCO_3(aq)$ to the sample; the evolution of $CO_2$ gas (fizzing) indicates the presence of a $-COOH$ group.

Mass Spectrometry

An analytical method used to measure the relative molecular mass of organic compounds by measuring the $m/z$ (mass to charge ratio) of accelerated positive ions.

Molecular Ion ($M^+$)

The ion formed when a molecule loses an electron but does not break up; its mass corresponds to the relative molecular mass of the compound.

Fragmentation

The process in mass spectrometry where molecular ions break into smaller ions due to bond breakage during ionisation, creating a unique 'fingerprint' for the compound.

High Resolution Mass Spectrometry

A technique that measures masses to three or four decimal places, allowing for the determination of a precise molecular formula based on exact atomic masses (e.g., $^{16}O = 15.99491$).

Gas Chromatography Mass Spectrometry (GCMS)

A powerful analytical combination where gas chromatography separates a mixture and mass spectrometry identifies and measures the amount of each component.

Infrared (IR) Spectroscopy

A technique used to identify functional groups by passing infrared radiation through a sample; specific chemical bonds absorb radiation at their unique natural frequencies.

Wavenumber

The unit of frequency used in infrared spectra, measured in $cm^{-1}$, which is proportional to frequency.

Transmittance

The measurement of the intensity of radiation emerging from a sample in an infrared spectrometer, plotted against the wavenumber.

Fingerprint Region (IR)

The area of an infrared spectrum below about $1500\,cm^{-1}$ containing many peaks caused by complex whole-molecule vibrations, unique to each substance.

$O-H$ absorption (Alcohols)

Produces a broad infrared peak between $3230$ and $3550\,cm^{-1}$.

$O-H$ absorption (Carboxylic Acids)

Produces a very broad infrared peak between $2500$ and $3000\,cm^{-1}$.

$C=O$ absorption

Produces a sharp infrared peak between $1680$ and $1750\,cm^{-1}$, common to aldehydes, ketones, and carboxylic acids.

Greenhouse Effect

The process where atmospheric gases like $CO_2$ and methane absorb infrared radiation via their chemical bonds, contributing to global warming.