Chemistry: 3.15 NMR
This flashcard set outlines three key analytical techniques—mass spectrometry, infrared spectroscopy, and nuclear magnetic resonance (NMR)—used to determine the structure of chemical compounds. It also explains the concept of nuclear spin, a property of atoms with odd mass numbers that enables NMR analysis.
which 3 techniques do chemistry use to deduce structure of compounds
mass spec
ir spec
NMR
Key Terms
which 3 techniques do chemistry use to deduce structure of compounds
mass spec
ir spec
NMR
what does NMR stand for
nuclear magnetic resonance
what is the property called that atoms with an odd mass number have
nuclear spin, can behave like tiny magnets
what do atoms with an odd mass number in sample do when placed ina a magnetic field
either align with or against magnetic field
resonance
combination of magnetic field and radio frequency radiation causes nuclei to absorb energy and flip between the two nucear spin states
what do nuclei in different chemical environments require different amounts of
energy to flip between states
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| Term | Definition |
|---|---|
which 3 techniques do chemistry use to deduce structure of compounds | mass spec ir spec NMR |
| nuclear magnetic resonance |
what is the property called that atoms with an odd mass number have | nuclear spin, can behave like tiny magnets |
what do atoms with an odd mass number in sample do when placed ina a magnetic field | either align with or against magnetic field |
resonance | combination of magnetic field and radio frequency radiation causes nuclei to absorb energy and flip between the two nucear spin states |
what do nuclei in different chemical environments require different amounts of | energy to flip between states |
what can the energy required to cause resonance be | detected and processed to give NMR spectrum |
solvent | deuterated solvents such as CDCL3 are used |
reference | tetra methyl silene |
where does TMS standard appear in NMR spectrum | 0ppm |
why is TMS suitable standard to use | inert, non toxic, volatile 12 equivalent Hs- one strong, sharp signal |
what scale do chemists use to compare the positions of peaks in an NMR spectrum | chemical shift |
what are the units of chemical shift | ppm |
what does the chemical shift of a particular nucleus depend on | its molecular environment |
C13 NMR: number of peaks = | number of different carbon environments |
C13 NMR: chemical shift tells us | type of chemical environment of particular carbon atom |
proton NMR: number of peaks = | number of different hydrogen environments |
proton NMR: chemical shift = | type of chemical environment of particular H atom |
proton NMR: integration provides information on | number of protons in a particular environment |
| number of protons bonded to adjacent C atoms |
proton NMR: what does relative area of a peak relate to | number of protons in that particular environment |
proton NMR: why are the relative heights of each integration trace also proportional to the number of H atoms in each environemtn | because they themselves are proportional to the peak area |
proton NMR: what is peak splitting sometimes referred to and why | caused by spin-spin coupling and is sometimes referred to as spin-spin splitting |
proton NMR: singlet | no adjacent protons |
proton NMR: doublet | one adjacent proton |
proton NMR: triplet | 2 adjacent protons |
proton NMR: quartet | 3 adjacent protons |
proton NMR: which protons usually don't split | OH and NH |