Proton NMR Flashcards
(20 cards)
What is NMR
Analytical technique that allows the structure of a molecule to be determined by analysing the energy of each bond environment, dif bond environs within molecule absorb dif amounts of energy so are displayed as dif peaks on spectra
What are bond environment peaks measured against
Standard molecule TMS Si(CH3)4 as it contains four identical carbon and hydrogen environs so can be easily identified as seen as peak at delta = 0ppm on x axis
What is sample dissolved in and placed in
Deuterated (even number nuclei hydrogen isotope) solvents eg CDCl3 or solvents without hydrogens eg CCl4 as solvents with hydrogen atoms in them will produce peaks in the spectrum
-placed in long thin tube inside machine where bombarded with radio waves in strong magnetic field
What does number of peaks in proton NMR show
The number of hydrogen environments
What atoms show in NMR
Those with odd atomic/mass number so overall nuclear spin, when this nucleus placed in a magnetic field the small magnetic field generated by the nuclear spin can be aligned with or against the main magnetic field and if radio waves passed through the substance some frequencies of radio waves will be absorbed to flip the nucleus from one spin direction to the other
How many equivalent hydrogens in propane and ratio
2 sets of equivalent hydrogens, ratio 6:2 (3:1)
Why is TMS used
As it only gives one signal, is non toxic and inert, has low bp so can easily be removed from the sample afterwards and gives a signal that is further right than most of the signals from organic compounds
What is x axis of spectra and what does this mean
Chemical shift, how far the signal is away from the signal for TMS in ppm
What does chemical shift of hydrogen atoms depend on
What other atoms/groups are near it, the closer the H is to electronegative atoms or double bond/the more electronegative atoms near the greater the shift to the left
What does vertical axis of spectra represent
The intensity of the absorption
What does the area of the peak in proton NMR represent
Proportional to the number of H atoms it represents
How to show the relative size of the signals
Indicate the relative intensity of the signals (no hydrogens in equivalent environ) from which the simplest whole number ratio can be calculated
What rule do splitting patterns follow
n + 1 rule, n is the number of hydrogen on the adjacent carbons
What is a singlet
Zero hydrogen on adjacent carbon, just one line
What is a doublet
1 hydrogen on adjacent carbon, two lines half the length of singlet
What is triplet
Two hydrogens on adjacent carbon, two short lines with longer line between them
What is a quartet
Three hydrogens on adjacent carbon atom, two shorter lines with two longer lines between them
Does the H atom of the OH/NH group in alcohols cause splitting
No and is rarely split itself, sometimes appears as a broad hump
What is triplet-quartet splitting pattern commonly representing
CH2CH3 fragments
What splitting pattern indicates benzene ring
Complex multiplet
