Spectroscopy Flashcards
Says that the energy of electrons in atoms and molecules are quantized in specific allowed energy levels
quantum theory
Electrons, ___ or ___ are excited to higher electronic states by __ or ____ and then give off ___ as the electrons relax back from higher energy states to lower energy states. The difference between two of these allowed energy levels can be measured when a system ___ or ___ these photons of electromagnetic radiation
atoms, ions, heat, light, photons, absorbs, emits
Light consists of packets of photons of various wavelengths that have no ___, are ____ ___, have a ___ field, and have an ___ field
mass, pure energy, magnetic, electric
The electrons generate a magnetic field because it ___ and carries a ___. When there is an external magnetic field, the electron can orient its spin __ or ___ that field
spins, charge, with, against
All molecules have a series of _____ modes whose motion and hence __ are quantized. Complicated molecules may vibrate in a number of different ____. Vibrations can be excited by the absorption of electromagnetic radiation in the ____ region.
vibrational, energies, modes, IR
Typical energies for vibrational excitation are _____and the frequency of radiation absorbed should be ____
10E-20 - 10E-10, 10E13-10E14
The __ ___ ___ says that the electric dipole moment of the molecule must change during the vibration. ___ ____ are IR inactive since there can be no dipole moment change during their one and only __ ___, thus their vibrations do not absorb of generate radiation. ___ ___ will be IR active
gross selection rule, homonuclear diatomics, stretch mode, heteronuclear diatomics
The __ ___ __ ___ states that the change in vibrational energy between two states is always equal to ___. in other words, it vibrates one ___ higher when the photons have just the right amount of energy and the molecule absorbs ____
quantum mechanical selection rule, +1, unit, light
At room temperature, almost all molecules will be in their vibrational ___ ___, so the main spectral transition upon photon absorption will be from ___ to _____
ground state, v=1, v=0
For a molecule of N atoms, there are ____ vibrational. modes for polyatomic molecules and ____ modes for linear polyatomic molecules
3N-6, 3N-5
In an IR spectrum various absorption peaks correspond to the __, ___, ___ and ___ vibrational modes.
stretching, bending, rocking, wagging
Vibrations that don’t involve ____ have lower energy transitions and are found in the region below _____cm^-1. This region is called the __ ___ because it contains many distinctive peaks that can be used to identify ____, and contains all possible _____ vibrations of a molecule
stretching, 1500, fingerprint region, unknowns, bending
IR spectroscopy is used for the identification of __ ___ before NMR was invented, __ __ determination in organic and inorganic synthesis, in __ ___ where molecules are in the gas phase, in physical chemistry for determining __ ____, and for detecting very ___ amounts of material
molecular structure, functional group, atmospheric spectroscopy, bond strengths, small
Are _____cm^1 peak in an IR spectrum is indicative of a benzene ring
900-600
In UV/VIS spectroscopy, ___ are excited usually from a -__ or ____ molecular orbital to a nearby empty _______ orbital. The most probable electronic transitions occur from ___ to the ____.
electrons, bonding, nonbonding, antibonding, HOMO, LUMO
The photon energy wavelengths for the UV region is _____, and ___ for the VIS region
200-400, 400-700
The colour that we see are the photon frequencies that are ___ ___
not absorbed
The intensity of absorption is given by the __ __ ___
beer lambert law
UV/Vis show more _____ absorption bands compared to IR spectra. This is because electronic excitation happens much ___ than vibrations of atoms in the molecule. In a ___ transitions can be distinguished and show up as distinct absorption lines, while in liquids and solids, the transitions are mixed up, making it harder to distinguish ___ ____.
broad, faster, gas, individual vibrations
The ____ ____ ____says that faster transitions mean that nuclei do not respond fast enough for its ___ to change (in contrast to IR transitions where the geometry does change)
franck-condon principle, geometry
Most ___ ___ do not have colour. Organic molecules with ___ __ __ absorb light in the UV region. When conjugated double bonds form ___ or longer chains, the difference between the energy level of the HOMO and LUMO decreases. This results in the energy needed for electron transitions to ___, resulting in ___ wavelengths of absorbed light. This results in a switch from the UV to the ___ spectrum, making the molecule appear coloured
organic molecules, conjugated double bonds, 8+ , decrease, longer, vis
UV/VIS spectroscopy is used in ___ _____ __ ___ to examine the separated fractions of a mixture
high performance liquid chromatography
The part of the molecule that gives rise to the UV.VIS electronic absorption
chromophore
In organic chemistry, C-C ____ ____ and extended _____ series of double bonds, ____ ____, isolated ___ groups, and
carbonyls conjugated to extended ____ _____ are the chromophore. In inorganic chemistry, many coloured metal complexes occur for transition metals such as ___, ___, ___ and ___, due to electronic absorption by valence shell ___ electrons into LUMOS
double bonds, conjugated, phenyl rings, carbonyl, pi systems, Ni2+, Fe3+, Cu2+, Ti3+, d
Electronic transitions are usually referred to as
N to pi, N to sigma, Pi to pi, or sigma to sigma
When the UV spectrum is measured for a compound in the ___ phase, ____ fine structure can often be seen in electronic transition bands. Vibrational modes can slightly alter the ___ associated with electronic transitions. If the spectrum is measured in a solution, interaction with the ___ usually broadens the absorption peaks so a less detailed spectrum is obtained.
gas, vibrational, energies, solvent
___ bonds are very strong and electronic transitions from occupied sigma orbitals are very ___ ___ and not normally seen in the UV region. They can be measured by ___ ____.
sigma, high energy, x-ray spectroscopy
Pi bonds are ___ and transitions from occupied pi orbitals require energies that fall in the UV region. Thus, if a molecule absorbs in the UV/VIS region, there must be __ ___ present. ____ stabilizes the excited state more than the __ ___. The more conjugated double bonds there are, the lower the energy of the transition, and the ___ the wavelength of absorption.
weaker, double bonds, conjugation, ground state, longer
For aliphatic compounds absorption begins in the ___ region when there are ____ conjugated double bonds.
visible, 7
The red colour of blood is due to the highly conjugated ___ molecules of ____. ___ vs ____ vs _____ ___ poisoned blood have different UV/VIS spectroscopy
heme, hemoglobin, oxygenated, deoxygenaetd, carbon monoxide
In mass spectrometry, a substance is bombarded with an __ ___ that has sufficient energy to remove an electron from the molecule. The positively charged molecules that are produced, the __ ____ are ___ in a vacuum through a ___ ___ and are sorted on the basis of mass-to-charge ratio. Most ions produced into the mass spectrometer carry one positive charge, so the mass-to-charge ratio value is equal to their __ ___.
electron beam, radical cations, accelerated, magnetic field, molecular weight
The magnetic field will ___ the path of the charged molecules. The low or high mass ions are ____ and collide with an analyzer wall. Ions that are just the right charge-to-mass ratio follow the path of the analyzer and exit through the ___, colliding with the ___, which generates an electric current. This current is ___ and detected.
bend, deflected, slit, collector, amplified
By varying the strength of the __ __ the mass-to-charge ratio which is analyzed can be continuously varied.
external field
The most intense peak in a mass spectrum and the one that all others are reported relative to
base peak
The highest molecular weight peak will typically represent the __ __ minus an _____
parent molecule, electron
Small peaks observed above the calculated molecular weight are due to the ___ __ ___ of 13C, 2H, etc. __, ___, ___ and __ are the predominant isotopes, but some elements have two common isotopes. Elements with two common isotopes will have peak intensities that depend on the relative ___ of isotopes.
natural isotope abundance, 12C, 1H, 14N, 16O, abundance
Elements with ___ protons like alcohols or amines, can exhibit peaks at ___ or _____ instead of a molecular ion peak due to the loss or acquisition of ___ during ionization
labile, M-1, M+1, protons
Fragmentation occurs because of ___ ___in the charged molecule which breaks it apart into smaller fragments by breaking the ___ bonds in the molecule. The fragments that form are the most ___ charged species that a molecule can form. When a bond breaks in a radical cation, one fragment is ____, and the other keeps the original charge. Only the ___ fragment will generate a signal in the mass spectrum.
excess energy, weakest, stable, neutral, charged
If a molecule contains atoms with lone pairs of electrons, common for elements like __, ___, ___, ___, -__ and ____, or a structure that has excess electrons such as ___ __ or ___ ___, the radical cation splits at a bond adjacent to it. If there is no clear preference for one fragment to retain the charge, both fragment ions will be formed ___. Some fragmentation processes depend on the ability of molecule to assume __ __ ___
Br, O, N, Cl, S, P, aromatic rings, double bonds, statistically, cyclic transition states
An alkane molecular ion is relatively ___. the mass spec will show a series of ions corresponding to the loss of ___ groups. If it is branched it will show the same series but ions resulting from cleavage at the ____.
unstable, alkyl, branch
Alcohols have a weak molecular ion due to the loss of ____ and a loss of a ___ group. Thiols show a strong molecular ion because the loss of ___ is not as easy as the loss of water from alcohols. ___ show weak molecular ions because cleavage to form the +CH2NH2 ion is easy as positive charge is stabilized by ___ with the non bonded electrons on the nitrogen.
water, methyl, H2S, amines, resonance
___ compounds show a strong molecular ion, while carboxylic acids and esters show a loss of ___
aromatic, CO2
Mass spectrometry can now analyze big and small molecules and is important in the analysis of ___ ____.
biological compounds
Cleavage of straight chain carbons tend to happen at ___ points. Chain cleavage tends to occur at the second carbon from _____, __ ___ and __ ___. Cleavage also tends to occur at the carbon directly next to ____ groups to give stable __ ___. Cleavage may also occur right next to heteroatoms for example in the case of ___.
branch, heteroatoms, double bonds, aromatic rings, carbonyl, acylium cations, ethers
The degree of unsaturation is the number of __ __ in a molecule. It is given by the formula _____, where C is the number of carbons, X is the number of halogens and hydrogens, and N is the number of nitrogens
double bonds, C+1 - 1/2(X-N)
Any atomic nucleus that either has an odd __ __ or odd ___ __ has a quantized ___ ___ __ that is positively charged and thus has a magnetic moment associated with it. These nuclei behave as tiny magnets.
mass number, atomic number, spin angular momentum
Common nuclei that possess spin: ___, ___, ____, ____, ___, ___ and ___
1H (1/2), 13C(1/2), 19F(1/2), 2H(1), 31P(1/2), 14N(1), and 17O(5/2)
Common nuclei that are not magnetic are ___ and ___
12C, 16O (0)
The NMR active nuclei can be in ___ possible quantized spin states, ml. 13C and 1H have only two possible spin states, ____ or ___.
2l+1, +1/2, -1/2
the nucleus can spin with or __ the magnetic field. As the strength of the magnetic field increases, the difference in energy between the +1/2 and -1/2 spin states _____. Nuclear magnetic resonance occurs when this energy separation between the two spin states is matched by ___ of that electromagnetic radiation. When resonance absorption occurs, spins flip from _____ ___ __ state to __ __ ___ state and vice versa. NMR is the observation of the ____ at which magnetic nuclei in molecules come into resonance with an electromagnetic field
against, increases, photons, low energy alpha, high energy beta, frequency
An NMR spectrometer is a magnet that can produce a uniform, ___ ___. The size of the magnetic determines the __ of the magnetic field. It has appropriate sources of ___ to induce resonance.
intense field, strength, radiofrequency
in NMR nuclei align themselves either parallel or ___ to the external magnetic field. If a _____ is applied to the sample, it causes the aligned nuclear magnetic moments to ____ away from their original alignment. the rate at which the nuclear magnetic moments -__ around the axis of the external magnetic field is called the ___ ___ and is directly proportional to the strength of the external magnetic field and the -_ ____. In NMR we measure the absorption or emission of ____ ___ by nuclei as they undergo precession at larmor frequency.
antiparallel, radiofrequency, tilt, precess, larmor frequency, gyromagnetic ratio, radiofrequency energy
__ ____ is when the resonant frequency varies due to the local magnetic fields felt at the ___. This is due to the circulation of ____ around or nearby the nucleus, which can either cause a _____ effect, as it reduces the effective magnetic field felt at the nucleus, or a ____ effect, which increases the effective magnetic field felt by the nucleus. Nuclei tend to be deshielded by groups which ____ electron density. This will cause different nuclei of the same element in a molecule to come into resonance at different ____.
chemical shift, nucleus, electrons, shielding, deshielding, withdraw, frequencies
The reference compound, TMS, or ______, is a chemically ____ ___ who’s chemical shift is assigned 0. In this molecule, all protons have the same larmor frequency due to ___
(CH3)4I, unreactive liquid, symmetry
____ ___ occurs due to the fact that each proton can be in two magnetic spin states, which interacts with another proton’s __ __, causing the resonance to split. The observed nucleus can sense the presence of other nuclei with magnetic moments and are either slightly ___ or ___ depending on which state the other nuclei are in. Nuclei that sense other nuclei in an ___ state will have slightly different energy to those which sense other nuclei in a __ state
spin-spin couplling, magnetic field, stabilized, destabilized, alpha, beta
Coupling does not occur between different _____, and H-H coupling is generally unobservable across more than __ intervening bonds
molecules, 3
The spin-spin coupling constant is the ___ __ in Hz between the peaks in each split. It is ___ to ___ Hz, and independent of the ___ ___. Thus it indicates structural information. Splitting tend to disappear and be concentrated into a tight ____ when all the chemical shifts are about the same
frequency distance, 20, < 0, magnetic field, multiplet
The NMR signal of a nucleus coupled to N equivalent protons will be split into a multiplet with ___ lines
n+1
_____, ___, ____, ___ and sometimes ___ are labile or ___ protons, that often have ___ resonances, and often do not have reliable characteristic chemical shift ranges. Labile protons exchange rapidly with each other and also with protons in ___ or with the deuterons in ____.
R-OH, R-NH, RCOOH, R-SH, R-CO-NH, exchangable, broadened, water, D2O
13C spectroscopy is only ___ as sensitive as 1H to NMR as 13C is only ___% naturally abundant and has a low __ ____.
1/6000, 1.1, gyromagnetic constant
There are no spin-spin splitting between adjacent 13C, but the ___ atoms attached to the 13C atoms are strongly coupled. The J for sp3 is ___Hz, sp2 is ____, and sp is ____
H, 125, 160, 250
During ___ __, 1H is irradiated to ___ them from the 13C resonance. This improves the ____ ratio
broadband decoupling, decouple, signal/noise
The number of resonances in the 13C NMR is the number of distinct ____ ___. If it is less than the number in the molecule, the molecule must have some ____.
13C environments, symmetry
Chemical shifts in 13C NMR are ___ than 1H NMR due to the presence of shielding by ____ ___ ____, ie., non symmetrical electron clouds. Additionally the area under the singlets do not correspond to the number of carbons present in the molecule, thus there is no ____.
larger, non-spherical molecular orbitals, integration
In MRI, a linear gradient field causes ___ to resonate at different frequencies at every point along an ____ which produce a profile of the water container with the signal intensity being proportional to the amount of water at each point along the __ ___. This allows imaging of ___ ____ which is 60-70% water in 3D
water, axes, gradient direction, soft tissue
