Experimental Determination of Structure Flashcards
What is elemental Microanalysis used to determine
The masses of C,H,O,S and N in a sample of and organic compound, to find the empirical formula
What is an Empirical Formula
It shows the simplest ratio of the elements in a molecule
Elemental Microanalysis can be determined from….
- Combustion Product Masses
- Percentage Product by Mass
What is Mass Spectroscopy used for?
To determine the accurate GFM and structural features of an organic compound
Describe the Process of Mass Spectroscopy
- Small sample of organic compound id bombarded by high-energy electrons
- This removes electrons from the organic molecule, generating positively charged molecular ions known as parent ions
- These molecular ions then break into smaller positively charged ion fragments
How is the Mass spectrum obtained
A mass spectrum is obtained showing a plot of the relative abundance of the ions detected against the mass-to-charge (m/z) ratio
The mass-to-charge ratio of a parent ion can be used to determine…..
The GFM of the molecular ion and so a molecular formula can be determined using the empirical formula
What is Infrared Spectroscopy is used to identify?
Certain functional groups in an organic compound
What happens when infrared radiation is absorbed by organic compounds
Bonds within the molecule vibrate (strech and bend).
The wavelengths of infrared radiation that are absorbed depend on…..
the type of atoms that make up the bond and the strength of the bond
What os the absorbance of infrared radiation measured in?
Wavenumbers (reciprocal of wavelength) in units of cm^-1
What happens in infrared Spectroscopy
Infrared radiation is passed through a sample of the organic compound and then into a detector that measures the intensity of the transmitted radiation at different wavelengths
What does proton NMR stand for
Proton nuclear magnetic resonance spectroscopy
What does Proton NMR tell you
NMR Gives information about the different Chemical Environments of hydrogen atoms in an organic molecule, and about how many hydrogens there are in each of the environments
How does NMR Work
- H nuclei behave like tiny magnets and in a strong magnetic field some (lower energy nuclei) align with the field , whilst the rest align against it (higher energy nuclei).
- Absorption of radiation in the
radio frequency region of the electromagnetic spectrum causes the H nuclei to ‘flip’ from the lower to the higher energy alignment. - As they fall back from the higher to the lower energy alignment the emitted radiation is detected and plotted on a spectrum.
What does the Chemical Shift in NMR tell you
Is related to the environment of the H atom and is measured in parts per million
What does the area under the paek of an NMR tell you
- The area under the peak is related to the number of H atoms in that environment and is often given by an integration curve on a spectrum.
- The height of an integration curve is proportional to the number of H atoms in that environment, and so a ratio of H atoms in each environment can be determined.
What is Tetramethylsilane’s (TMS) chemical shift value?
0
H NMR spectra can be obtaoned using what type of resolution NMR
High and Low
Benefits of high resolution NMR
High-resolution H NMR uses higher radio frequencies than those used in low-resolution H NMR and provides more detailed spectra.
Describe high resolution NMR in terms of peaks
In a high-resolution H NMR an interaction with H atoms on neighbouring carbon atoms can result in the splitting of peaks into multiplets.
The number of H atoms on neighbouring carbon atoms will determine the number of peaks within a multiplet and can be determined using the n+1 rule, where n is the number of H atoms on the neighbouring carbon atom.
What is a benefit of low-resolution NMR
Spectra can be sketched for any given compound
