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
Purpose of Chromatography
Qualitative: determine the unknown components of a sample based upon its unique retention time
Qualitative: determine how much of a sample is produced (but requires a calibration curve)
Principles of Chromatography
Each substance will have a unique retention time (time taken to flow through the column), based upon:
The attraction to its stationary phase (adsorption)
The attraction to its mobile phase (desoprtion)
Does Chromatography destory the sample
No
Mobile Phase
What the components of the sample dissolve into
Stationary Phase
The surface that the mobile phase (and the sample) flows over
What is HPLC
A chromatography technique - consists of a solid stationary phase, which is tightly packed into a glass column and a solvent that acts as the mobile phase
What is Retention Time
The time taken for a component to pass through the column - depends on the extent to which the sample is attracted to the stationary vs the mobile phase
Influence of a Longer Column on Retention Time
Will increase retention time
as it will take more time for the sample to flow through the column
Influence of Increased Temperature on Retention Time
Will decrease retention time
as an increase in temperature increases the solubility of most substances (excluding gases) - which results in the substance being more strongly adsorbed into the mobile phase
Influence of Increased Flow Rate of the Mobile Phase Retention Time
Decreases Retention Time
As the mobile phase is able to flow through the column faster, which will result in the sample flowing faster
Influence of increasing surface area of the stationary phase on Retention Time
Increase Retention Time
Increased surface area results in stronger intermolecular bonds (greater surface for interactions), this results in the sample being more strongly adsorbed to the stationary phasei
Purpose of Titration
Quantitative: to determine the unknown concentration of a solution
Titration - Titrant
Solution of known concentration - placed into the burette
Titration - Analyte
Sample solution of unknown concentration - placed into the conical flask
How is a titrant conducted
The titrant is dispensed incrementally from the burette, and reacts gradually with the analyte.
This process continues until the change in color occurs (endpoint) - which can be seen with the presence of an indicator
Titration - Equivalent Point
the point at which the titrant and the analyte have reacted to the stoichiometric ratio indicated in the balanced chemical equation
Occurs normally just after the endpoint (however - for the purposes of calculations we assume the endpoint is a good approximate of equivalence point)
Titrations - Titre (and Concordant Titre)
Titre - the volume of titrant that is used to reach the endpoint
Concordant Titres - titres that are close together (usually within +-0.1mL(
Neutralization Reaction
Acid + Base -> Ionic Salt + Water
Acid - Base Titration (+ what to use for an indicator)
Determines the concentration of acids or bases via a neutralisation reaction between the two substances
For an indicator: use an indicator that falls within the pH of the equivalence point
Equivalence Point for Acid/Base Titrations
Redox Titrations (+ what to use for an indicator)
Redox Reaction between the oxidizing and reducing agent
For an indicator: often the reaction itself involves substances that change color as a result of the redox reaction - which means they may not require the use of an indicator
Exceptions: for reactions involving iodine - use starch as an indicator
