U4AOS1 - Analysis of Organic Compounds Flashcards
What is the purpose of Mass-Spectroscopy
To measure the mass-to-charge (m/z) ratio of a molecule in a sample
Quantitative: shows the molecular mass of a sample
Qualitative: can provide insight into the branching of the molecule
How does Mass-Spectroscopy work?
Molecules are placed in a mass-spectroscopy machine, where they are ionized, producing positively charged fragments
The fragments produced may be the entire molecule, or a component of the molecule
Important thing to write with a fragment from Mass-Spec
Ensure that the molecule is positively charged (because its been ionized)
Molecular Ion Peak (on MS)
the largest peak on the graph - represents the full molecule (positively charged)
Base Peak (on MS)
the most abundant fragment (often created by a single split in the molecule) - assigned a relative abundance of 100%, with other fragments measured against it
Impact of Isotopes
Given isotopes have differing numbers of neutrons, they will appear at different m/z peaks on a mass-spec graph (could sometimes be higher than the ion peak)
They will generally have a small relative abundance relative to their low appearance in nature
X Axis of Mass Spectrum
Mass-to-Charge Ratio
Y Axis of Mass Spectrum
Relative Abundance
Purpose of Infrared Spectroscopy
Qualitative - to determine the bonds and the functional groups in an organic molecule
Quantitative - to determine the concentration of a solution
Principles of Infrared Spectroscopy
Different polar bonds absorb light at different wavelengths
Therefore - you can determine the bonds and functional groups by detecting which wavelengths of light are absorbed
X Axis of Infrared Spectra
Wavenumber (cm^-1)
Y Axis of Infrared Spectra
Transmittance (%)
Fingerprint Region
between 500-1400cm^-1
Unique for each molecule - don’t need to know how to read in VCE
Finding Hydroxyl Groups on Infrared Spectra
Roughly 3000-3400cm^-1
Carboxyl Acids - will be broad, and stretch below 3000cm^-1
Alcohols - will be above 3000cm^-1, and be skinner
Finding Carbonyl Groups on Infrared Spectra
Swords roughly between 1650 and 1850cm^-1
Finding N-H groups on Infrared Spectra
Swords at 3300-3500cm^-1
Primary Amine/Amides will have a single fang
Secondary Amine/Amides will have a single fang
Purpose of NMR
Quantitative: number of chemical environments environments
Quantative: ratio of atoms in an organic compound
Nucleus Spin States
A nucleus, with protons and neutrons, is able to behave like a magnet - in the absence of an external magnetic field, the nuclei will be randomly oriented
When a nucleus is placed in an external magnetic field (B0), it will either align with (low energy level) or against the field (high energy level)
The electrons around the nuclei oppose the external magnetic field, shielding the nucleus from its effect
Principles of NMR
A compound is placed within an external magnetic field, and the energy required to create a spin flip is recorded
Use of TMS in NMR
TMS - tetramethylsilane, (CH3)4 Si)
An inert substance that will only produce a single peak
All other energy levels will be compared against TMR
X Axis of NMR Spectra
Represents the chemical shifts (measured in ppm)
Peaks in NMR Spectra
Represents a unique carbon/hydrogen environment
H NMR Splitting Pattern
Because H NMR is high resolution, the peaks will split in accordance with the (n+1) rule
where n represents the number of hydrogens on the adjacent carbons
H NMR Area under Peaks
the ratio of the area under the peaks can be used to determine the ratio of hydrogens in each particular hydrogen environment
