Spectroscopy Flashcards
What are the features of mass spectrometry?
- Determines relative atomic masses and relative abundances of isotopes.
- Also used to analyse molecules like organic ones.
- It breaks molecules into ionized fragments
- Maybe detected and displayed as a spectrum - can give you molecular mass and structure info.
What’s the process of fragmentation?
- Molecule peppered with high energy electrons which makes it lose an electron.
- Forms positive ion and it absorbs energy.
- Causing it to break into fragments.
- Positively charged fragments appear in the mass spectrum.
What causes the tallest spectrum’s peak?
Fragment being produced in greatest quantity.
What’s the spectrum peak called?
Base peak.
What are other peaks on the spectrum measured as?
Abundances of other peaks on the spectrum are measured as a percentage of the base peak abundance.
What are features of molecular ion peaks?
- Produced by a molecule losing an electron.
- Mass at which molecular ion peak is found represents relative formula mass of a molecule.
- It is normally found in the cluster of peaks of greatest mass on the spectrum.
- Can be very weak or even absent.
What are the key points of the spectra?
- M+1 shows number of carbon atoms present in a molecule.
- M+2 peak identifies compounds containing chlorine and bromine.
- A molecular ion of old mass suggests the presence of nitrogen.
- The fragmentation pattern produced is characteristic of the molecular formulae structure.
What does UV/Vis spectroscopy detect?
Electronic transitions between molecular energy levels.
What creates a single covalent bond?
Formation of a sigma
What does a double bond involve?
Formation of a pi molecular orbital.
What is an unfavourable energy level always formed along with?
An unfavourable energy level called an antibonding orbital is always formed along with a bonding orbital.
What does the energy required to make an electrostatic transition in a molecule depend on?
How strongly the electrons are attracted by the nuclei of bonded atoms.
What is the characteristic energy in transition a property of?
A group of atoms.
What’s a chromopore?
A group of atoms producing such a characteristic absorption.
Features of infared spectroscopy?
- Used to detect vibrational transitions.
- For a band to be infared-active it must have an electric dipole that changes as it vibrates.
- When molecules absorb radiation of infared wavelengths it causes a change in the modes of vibration.
- The simplest modes of vibration are stretching and bending.
