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32 Cards in this Set
- Front
- Back
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What is the study of spectroscopy? |
-Spectroscopy is the study of the interaction between matter and radiated energy. -An important tool in determining chemical structures. |
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How can we determine chemical structure with spectroscopy? |
-The amount and type of light absorbed depends on the nature of the chemical structure, bond types and electric structure. -We can measure this and determine the nature of the chemical. |
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What is a wavelength? |
The distance between any two consecutive equivalent points on a wave. |
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What is frequency? |
Frequency is the number of full cycles of a wave in a second. |
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What is the relationship to wavelength and frequency? |
Wavelength is inversely proportional to frequency. |
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As wavelength increases, what happens to frequency and energy levels? |
-As wavelength increases, the frequency and energy decreases. -Wavelength and frequency are inversely proportional. |
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What is infrared spectroscopy? |
Infrared spectroscopy observes the vibration of covalent bonds by absorbing infrared energy. |
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What happens to covalent bonds when they absorb energy? |
Covalent bonds bend and stretch when they absorb energy. |
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What wavenumber represents the carbonyl (C=O) group? |
The carbonyl group is represented by a wavenumber between 1700-1730cm⁻¹. |
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What wavenumber represents the O-H functional group? |
The O-H functional group is represented by a wavenumber between 3000-3400cm⁻¹. |
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What wavenumber represents the N-H group? |
The N-H group is represented by a wavenumber between 3000-3400cm⁻¹. |
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What wavenumber represents nitriles (C≡N)? |
Nitriles (C≡N) are represented by a wavenumber ~2000cm⁻¹. |
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What is nuclear magnetic resonance (NMR) spectroscopy? |
-NMR observes nuclear spin changes when radio frequency (200-900MHz) energy is absorbed in the presence of a magnetic field. -This gives numbers & type of atoms in a molecule. |
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What happens when an atomic has an odd atomic number or atomic mass (or both)? |
-An atomic with an odd atomic number and/or mass has a quantum nuclear spin of 1/2. -This spin creates a small magnetic field. |
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Which way does nuclear spin occur? |
-Nuclear spins are completely random in orientation. -In an applied field, a small majority of nuclear spins are aligned with the applied field. -The larger the applied magnetic field, the larger the energy difference between nuclear spins with aligned field and nuclear spins against aligned field. |
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What happens when a spinning nuclei is irradiated with electromagnetic energy equal to the energy difference (between nuclear spin and applied magnetic field)? |
This causes a spin flip (excitation). |
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What are equivalent protons? |
Equivalent protons are identical in every way. Same magnetic environment, and the same spin flip energy (ΔE). |
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Why do equivalent protons need to be identified? |
The number of signals found in NMR corresponds with the no. of nonequivalent protons in a molecule. |
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How is proton equivalence determined? |
-Identify a mirror plane in the molecule. -Identify the axis of rotation. If the molecule looks the same upon rotation, the protons are equivalent. -Identify what atoms the protons are connected. If these atoms are directly connected to the same atom, they are equivalent. -If they differ by even one atom, they are non-equivalent. |
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A molecule with all equivalent protons has a NMR number of? |
A molecule with all equivalent protons has a NMR number of 1. |
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What is a carbon signal? |
The carbon signal is the number of variations of carbon atoms found in a molecule. ie. C----CH3 has a carbon signal of 2. |
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What is mass spectroscopy (MS)? |
-MS is an analytical technique that detects ions produced by high energy electrons. -High energy electrons bombard a molecule and pushes out other electrons (giving the molecule an increased positive charge). |
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How can the mass spectrum show the molecular weight of a molecule? |
The mass spectrum can show molecular weight by the amount of light absorbed. |
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What is hydrogen deficiency (HD)? |
The sum of the number of rings and pi bonds in a molecule. ((2n + 2) - H molecule)/2 = index of hydrogen deficiency. |
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What is H reference? |
-The basic H reference used in the hydrogen deficiency is C(n)H+2. -For example, C6H14 = 2(6) + 2 = 14. |
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What happens to the H reference when C(n)H+2 is bonded with a group 17 atom? |
-When C(n)H+2 is bonded with a group 17, minus 1 H from the equation. C(n)H+2 -> 2n+2 C(n)H+2Cl-1 -> 2n+1 |
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What happens to the H reference when C(n)H+2 is bonded with an atom from group 16? |
-When C(n)H+2 is bonded with a group 16 atom, no correction is necessary. C(n)H+2 -> 2n+2 C(n)H+2O -> 2n+2 |
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What happens to the H reference when C(n)H+2 is bonded with an atom from group 15? |
-When C(n)H+2 is bonded from a group 16 atom, add +1 to the hydrogen. C(n)H+2 -> 2n+2 C(n)H+2N+1 -> 2n+3 |
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What happens to compounds that absorb light in the UV/visible region? |
These compounds go from higher occupied molecular orbital (HOMO), to the lowest unoccupied molecular orbital (LUMO). |
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What are the two conditions that a molecule must fulfill for it to absorb UV-vis light? |
-It must contain either a pi bond or atoms in a non-bonding orbital (a lone pair). |
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What is the Beer-Lamberts law? |
Beer´s law relates the amount of light absorbed to the concentration of a substance absorbing energy. A=εcl A=absorbtion c=molar concentration (mol/dm³) l=path length ε=molar extinction coefficient of a sample (dm³mol⁻¹cm⁻¹). |
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What is X-ray crystallography? |
-X-ray crystallography is the study of crystal structures through X-ray diffraction techniques. -X-ray causes crystalline atoms to diffract into many specific directions, generating a pattern. -the angles and intensities of diffracted beans produce three dimensional picture of electron density in crystal. -electron density determines positions of atoms as well as chemical bonds/structure of molecules. |
