Organic Chemistry: Experimental Determination of Structure

Section 1: Structural Determination in Organic Chemistry

Structural determination in organic chemistry involves identifying the molecular structure and arrangement of atoms within a compound.
Different techniques used for this include mass spectrometry, infrared spectroscopy (IR), and nuclear magnetic resonance spectroscopy (NMR).
These investigative techniques provide valuable information about the functional groups and overall structure within an organic compound.

Section 2: Mass Spectrometry

Mass spectrometry is a technique that is used to determine the molecular mass of a compound.
It works by ionising the samples, and then separating and measuring these ions based on their mass-to charge-ratio.
The resulting data is displayed in a mass spectrum graph, showing peaks corresponding to various ion fragments.
The highest peak, known as base peak, represents the most stable and abundant ion, while the peak furthest to the right, known as molecular ion (M), gives the molecular weight of the sample.

Section 3: Infrared Spectroscopy

Infrared spectroscopy is a tool used to identify functional groups in a molecule.
This method involves passing infrared radiation through a sample, which causes different bonds within the molecule to vibrate at characteristic frequencies.
These vibrations are plotted on an infrared spectrum as intensity versus frequency, also given in terms of wavenumbers.
Wavenumbers are specific to different types of bonds and functional groups, allowing for their identification. A reference table of known wavenumbers for different bonds is usually used.

Section 4: Nuclear Magnetic Resonance Spectroscopy

Nuclear Magnetic Resonance (NMR) spectroscopy helps ascertain detailed information about the structure of a molecule, including positions of atoms and the types of environments of hydrogen atoms in the molecule.
It works on the principle that nuclei of certain atoms, including hydrogen (H) and carbon-13 (C-13), absorb and re-emit electromagnetic radiation in a magnetic field.
The re-emitted radiation is recorded as different peaks in the NMR spectrum, each corresponding to different types of protons or carbons in the molecule.
The distance between these peaks, known as chemical shift, and the area under each peak, referred to as integration, provide valuable insight into the structure and number of protons in various environments of the molecule.

Section 5: Utility of Structural Determination in Organic Chemistry

These experimental spectrometry and spectroscopy techniques offer reliable ways to determine the structure of an unknown organic compound.
They form the backbone of structure elucidation in organic chemistry, aiding the development of new compounds in medicine and industry.
Understanding how these techniques function is crucial for anyone seeking a deeper understanding of the structure-function relationships in organic chemistry.