Spectroscopy & Analytical Methods Flashcards
True or false:
The perceived color of a substance is complementary to the color of the wavelength that was actually absorbed by the substance.
True
A substance which appears green, absorbs what color and wavelength range?
Absorbs red light ranging from 650-740 nm.
The difference between the HOMO and the LUMO, is inversely proportional to (energy/wavelength).
Wavelength; the higher the difference between the states, the higher the energy of the photon.
If the photon has high energy, its wavelength is decreased (short).
How does conjugation affect wavelength properties of a photon?
Conjugation makes a molecule more stable, so there is a lower energy. Lower energy means you have a longer wavelength.
What causes a solution to change color?
The electronic structure of the molecule in the solution changes. Basically, the wavelength/color that the solution can absorb depends on the electronic structure (electrons in the solution).
What does IR spectroscopy specifically measure?
The frequencies of electromagnetic radiation absorbed by molecules, the different molecular vibrations
What are the different vibrations IR spec can detect?
Bond stretching, bond bending, twisting & folding
What can you detect with IR Spec?
The presence of specific functional groups and connectivity of bonds (backbone) of a molecule
Define the fingerprint region
The the area of the IR spectrum between 500 and 1450 cm-1. It is unique and complex for every molecule, and is used to identify a specific molecule by chemists.
FG with a peak ranging from 1810-1650 cm-1 is?
C=O, carbonyl group
Aldehydes have a very strong characteristic peak at this specific range:
1740-1720 cm-1
What are the IR peaks for the sp, sp2, and sp3 carbons?
OH group from an alcohol absorbs at what frequency vs. an OH from a carboxylic acid
- Alcohol - broad peak 3300 cm-1
- Carboxylic Acid - very broad peak 3000-2400 cm-1
A sharp peak at 3300-3400 cm-1 indicates
An N-H bond
A general rule in IR spec is that heavier atoms, record lower wavenumbers because they have slower frequencies.
Which bond will have a higher wavenumber:
C-H
C-N
C-H
UV-Spec measures the absorption of ______ causing electronic excitations that distinguish the different bonds.
UV-light
UV-Spec is specifically designed to analyze what kinds of molecules ?
Conjugated systems
-Double & triple bonds
Molecules (heteroatoms) with nonbonding pi electrons
Molecules containing transition metals
In proton NMR, how can one determine the amount of splitting of a single peak?
Look at your proton of reference, count the # of adjacent protons around it and use the (n+1) rule to determine the splitting.
n = # of adjacent protons
If you have a molecule with a plane a symmetry, how do you determine how many unique proton signals there are?
- Draw the plane of symmetry
- Count the H’s on each carbon ONLY on one side of the plane
- Example: in this compound, there are only 3 unique hydrogens due to plane of symmetry
When asked to find the integration of a specific peak, how do you go about this?
Assuming you are given a drawing of the molecule, count the # of protons corresponding that specific chemical environment.
In this example there are 4 H’s for environment A, which means the integration will be 4. If there are multiple chemical environments, there will be multiple peaks on the NMR.
What are the isotope signature mass specs of carbon, bromine, and chlorine?
How do you figure out the dilution factor?
What happens is there are two dilutions in sequence?
Final volume/initial volume = factor
If several dilutions happen in sequence, multiply the factors together to get a final dilution
True or false:
The higher the concentration in solution, the lower the intensity of light that is transmitted through the solution.
True, concentration and transmittance are inversely related.
