lecture 2 - Spectroscopy Flashcards
What is spectroscopy?
the interaction between light and matter as a function of a wavelength
what is a spectrum?
a plot of the response as a function of the wavelength (x-axis = wavenumber & y-axis = absorption)
what is spectrometry?
the measurement of these responses
what is infrared spectroscopy?
a technique that is used to identify which functional groups are present in a molecule. Functional groups appear at set frequency ranges and these peaks can have characteristic shapes and intensities.
are photons stable or unstable?
unstable
what does the electromagnetic spectrum consist of?
polychromatic radiation - multiple wavelengths separated into regions
what is the UV electromagnetic spectrum region?
190-400nm
what is the visible light region for violet, indigo, blue, green, yellow, and orange
violet = 400-420, indigo = 420-440, blue = 440-490, green = 490-570, yellow = 570-585, orange = 585-620
what is absorption spectroscopy?
the substance absorbs e.g. infrared
what is emission spectroscopy?
the substance radiates e.g. spectrofluorometry
what is scattering spectroscopy?
the amount of light a substance scatters e.g. Raman spectroscopy
what is Beer Lamberts law?
absorbance is directly proportional to concentration
what is the Beer lamberts formula and what does each letter represent?
A=ECL
A = absorbance, E = molar extinction coefficient, C = concentration, L = pathlength
why does absorption occur?
as a result of change of vibrational and rotational levels
what does low energy absorption equal?
molecular rotations
what does high energy absorption equal?
molecular vibrations
what does vibrational energy depend on?
the arrangement of atoms, masses of atoms, bond distances, and strengths of bonds
what is the second beer lamberts law?
A = -log I/Io
which are stronger bonds; sigma or pie?
sigma
what is an aliphatic hydrocarbon
a hydrocarbon with only single bonds which are very hard to break
which type of transition requires the most energy?
σ – σ*
what does a monochromator do?
acts as a filter which turns polychromatic light into monochromatic light
what does n – π* and π – π* have in common
the presence of unsaturated functional groups
what is the fingerprint region in IR spectroscopy
the area where the peaks are specific to each molecule = 600-1600cm-1
what does IR spectroscopy tell us?
molecule composition
what is absorption due to in IR spectroscopy
stretching or bending
what is the definition of stretching in terms of molecular vibrations and what does it cause.
vibration or oscillation along the line of the bond - causes the distance between two atoms to increase or decrease but they remain in the same bond axis
is stretching asymmetrical or symmetrical
both - but IR spec is only asymmetrical because symmetrical does not cause a change in polarity and therefore will not show up in IR spectra
in terms of molecular vibrations, what is bending and what does it cause
vibration or oscillation not along the line of the bond - it causes the position of atoms to change with respect to the original bond axis
what are the 4 types of bending
scissoring, rocking, wagging or twisting
what is the molecular vibrations formula for linear molecules
3n-5, where n is the number of atoms
what is the molecular vibrations formula for non-linear molecules
3n-6
name 4 reasons why the observed vibrations can differ from the predicted number produced from the equation
symmetry, energies of vibration are identical, absorption intensity too low, frequencies beyond range of instrument
a large U-shaped peak found between 3500-3200 is which functional group
the O-H bond of an alcohol
a large V-shaped peak found around 3000 is which functional group
the O-H bond in carboxylic acids
2 peaks found between 3500-3300 and is similar to a W is what functional group
a primary amine
a short peak found between 3500-3300 and is V-shaped is what functional group?
secondary amine
how many IR vibrations does carbon dioxide have and what are they called
4
symmetrical stretch, asymmetrical stretch, horizontal bending and vertical bending
