Chapter 13 Flashcards
What is the molecular ion?
M+1 and M+2 peaks?
The mass of the molecular ion is equal to molecular mass of the compound.
The molecular ion has the highest mass in spectrum, besides from isotopes. It is also the radical cation.
M+1 and M+2 account for isotopes.
What is the Nitrogen rule?
A compound with an odd number of N atoms will have an odd molecular ion and a compound with an even number of N atoms will have an even molecular ion.
What is the base peak?
The tallest peak in a mass spectrum
Mass spectrum of monochloride
Shows two peaks for the molecular ion in a 3:1 ratio. (One at molecular ion peak and other at M+1 peak)
Mass spectrum of monobromide
Shows two peaks for the molecular ion in a 1:1 ratio. (One at molecular ion peak and other at M+1 peak)
What are the lower molecular weights shown in a mass spectrometer?
They are fragmentation a of radical cations that have lower molecular weights. Usually functional groups
Difference between high and low resolution mass spectrometry
High resolution gives the molecular mass exactly( decimals), can tell us molecular formula.
Low resolution gives molecular mass in whole numbers.
Relationship between wavelength and frequency
Wavelength and frequency are inversely related. As one increases other decreases.
λ=c/ν
Relationship between energy and frequency
Energy of a photon is proportional to its frequency. The higher the frequency the higher the energy.
E=hν
What is infrared spectroscopy?
Records frequencies of compounds that identify functional groups and different types of bonds
IR absorption are reported in?
Wavenumbers 1/λ
Wavenumber a are proportional to higher frequencies and energies
C-H, O-H, N-H bonds absorb at low or high frequency?
High frequency. (>2500)
As bond strength increases the wavenumber increases or decreases?
Increases. Triple bonds absorb at higher wavenumber than double bonds.
The higher the percent s-character the lower of higher the wavenumber?
Higher. Bond strength increases with higher s-character.
What is mass spectrometry?
Measures the molecular weight of a compound. Also plots the molecular cations and fragments vs their mass
For absorption to occur in an IR spectroscopy the energy of a photon must what?
The photon must match the difference between the two energy states in a molecule
Absorption of IR light detects what changes in a molecule?
Vibrational motions of a molecule, including bending and stretching. Different kinds of bonds vibrate at different frequencies.
Absorption frequencies in IR spectroscopy depend on which two factors?
Bond strength. Stronger the bond, higher the frequency.(Triple bonds strongest)
Atom mass. Lights atoms vibrate at higher frequencies. (Bonds to hydrogens always on left side of spectrum because light atom)
For a bond to absorb in IR there must be a change in what?
There must be a dipole moment (polar). If molecule is nonpolar there won’t be an absorption.(IR inactive)
