week3 Flashcards
(34 cards)
Mass spectrscopy
What used for?
EI mass spectroscopy is routinely used to determine the molecular weight of a compound.
Thus can tell composition by seeing what molecular wight show up
Mass spectrscopy
how?
How?
1. A sample of the molecules of interest are passed through an electron beam, ionising the molecules.
2. The impact removes electrons from the molecule to make it charged (ionised).
3. These charged molecules are then accelerated to a constant velocity and passed through the magnetic region.
In this zone they are deflected, with the degree of deflection related to the m/z ratio. This allows the mass to be determined.
mass spec types
resolution and isotope distributions
Mass spectrometry can be either high or low resolution, which can be incredibly important for distinguishing compounds of similar mass.
mass spec findings
m/z ratio which shows the mass of the fragment
can be close to each other if there is a different ismoers
chlorine occurs as a mixture of 75.77% 35Cl and 24.23% 37Cl (a 3:1 ratio).
Br naturally exists as a 1:1 ratio of 79Br:81Br.
mirco analysis what?
Microanalysis is the process in which a compound is combusted and the specific percentage of C, H, and O measured
example of microanaylsis
Worked Example
MS indicates m/z = 108 and microanalysis gives C, 78%, H, 7.4%, O = 14.6%.
Determine the molecular formula of the unknown
this formular wiegh sould be check with a mass spec weight
Index of hydrogen deficiency (double bond equivalents)
Information about the presence of rings or unsaturation (double or triple bonds) can be obtained from the molecular formula.
IHD= Href- Hmolecule
———————-
2
H ref= from a saturated molecule from
What is Chemical shift (δ)?
the quantity used in NMR spectroscopy to identify the positions of signals produced by the nuclei of a sample. The unit of chemical shift (δ) is parts per million (ppm)
What is 13C-NMR spectroscopy?
Nuclear magnetic resonance spectroscopy of carbon atoms within molecules. It provides information about the carbon-hydrogen enrovoments of a molecule
IHD changes with other molecules
group 5= N,P ect
ADD 1 H TO REF
Group 6 = O S Se
NO CORRECTION
group 7 = F Cl Br
subrtarct 1h FROM REF
IR spec
What?
The absorption of infrared radiation provides information regarding functional groups in a molecule.
Dips in the graph indicate energy levels where bonds in the molecule have absorbed the IR energy
Results in the 1550-3800 cm-1 region are the most informative
whereas those
below 1400 cm-1 are generally too complex to be of use (FINGERPIRNT)
H NMR spec
Has TMS at 0
Breaks up hydrocarbon into parts to figure out what to do
Ratio of abundance from hight
Chemical shift analysed with WHERE peaks are from 0-8 ?
How does NMR work?
Atoms with spin not O are NMR active
IH and ‘3C have a spin = 1/2 (/= 1/2) and 2/+ 1 orientations in a magnetic field.
The more stable is aligned with the magnetic field
Radio-frequency energy flips spin to the less stable state.
How much depends on (1) the type of atom and (2) the strength of the magnetic field.
HNMR What does it tell us?
2 things
Chemical shift of proton environments
About functional groups and ones adjacent (splitting)
splitting
a hydrogen (proton)
a proton with n Neighbours will split into n+1 lines
if hydrogen atom has n other hydrogen atoms that are not equivalent to it, but are equivalent to each other, on the same or adjacent atom(s), its 1H-NMR signal is split into (n+1) peaks
how appraoch find what moleclue is questions
Use the following “work flow” to approach these types of problems:
1. What is the molecular formula?
2. What is the Index of Hydrogen Deficiency?
3. Does the IR spectrum indicate any functional groups?
4. From the number of signals (chemical shift and integration) in the 1H NMR and 13C NMR spectra, what
functional groups are present?
5. From the multiplicity in the 1H NMR spectrum, how are the functional groups connected?
6. From the chemical shift in the 1H NMR and 13C NMR, how are the functional groups connected?
CHECK. Does your structure match all the data?
What does deshielded mean?
describes the situation in NMR spectroscopy in which resonance or inductive effects reduce the electron density around a nucleus, thus increasing the ability of an applied magnetic field to bring the nucleus into resonance
What is a doublet?
a signal in 1H-NMR spectroscopy that has been split into two peaks in a ratio of 1:1
What does downfield mean?
Describe a signal in NMR spectroscopy that is towards the left of the spectrum or of another signal
What is high resonance mass specroscopy?
a technique that allows the precise measurement of the mas to charge ratio of ions
What is 1H-NMR spectroscopy?
nuclear magnetic resonance spectroscopy of hydrogen atoms within molecules. It provides information about the carbon-hydrogen framework of a molecule
What is integration?
a mathematical process used for determining the area under a signal in an NMR spectrum
curved line at a signal on a 1H-NMR spectrum that allows the determination of the relative number of hydrogen atoms giving rise to that signal
What is multiplicity?
the splitting pattern of a signal in 1H-NMR spectroscopy, which can be described as, singlet, doublet, triplet, quartet, multiplet etc.
What is a triplet?
a signal in 1H-NMR spectroscopy that has been split into three peaks in a ratio of 1:2:1
