Organic Chemistry II: Chapter 13
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88 Terms
spectroscopy is …
the study of the interaction of matter and light (or other electromagnetic radiation)
spectroscopy is important because it can …
be used to determine unknown molecular structures
electromagnetic radiation contains oscillating electric and magnetic field vectors that …
are perpendicular to each other
an electric field is capable of …
transferring energy to electrical charges, including charged atoms
a magnetic field is capable of …
transferring energy to magnetic dipoles, which we can think of as tiny bar magnets
wavelength is the distance …
between successive peaks or successive troughs
various forms of electromagentic radiation …
differ in their wavelength
red light has a wavelength of …
6800A
blue light has a wavelength of …
4800A
ultraviolet light has …
smaller wavelengths than blue light
microwaves have …
much greater wavelengths than visible light
the frequency of a wave is the …
number of wavelengths that pass a point per unit time when the wave is propagated through space
frequency is equal to …
the velocity of light / wavelength
‘E’ is the …
energy of a photon
a photon is a …
light particle
E = …
h(v) or hc/λ
h is Planck’s constant which equals …
6.626 × 10^-34 Js
the frequency and energy …
increase as the wavelength decreases
in absorption spectroscopy, the amount of absorption of energy …
varies with the wavelength of the radiation used
in an absorption spectroscopy experiment, you must use …
a spectrometer
an absorption spectroscopy experiment requires …
a source of electromagnetic radiation, a sample that is placed in the radiation beam, and a detector that measures the intensity of the radiation that passes through the sample unabsorbed
in order to find the amount of radiation absorbed from an absorption spectroscopy experiment, you must …
subtract the intensity of the unabsorbed radiation by the intensity of the source
Infrared (IR) spectroscopy provides …
information about what functional groups are present
Nuclear Magnetic Resonance (NMR) provides …
information about the number, connectivity and functional-group environments of carbon and hydrogen
Ultraviolet-visible (UV-vis) provides …
information about the type of pi-electron systems that are present
Mass Spectrometry allows us to …
determine molecular masses and is NOT a type of absorption spectroscopy
in IR spectroscopy, the unit of wavelength used is …
micrometer
wavenumber (ν̃) is the …
inverse of the wavelength (1/λ)
the unit of wavenumber (ν̃) is …
inverse centimeters (cm^-1)
in infrared radiation, the wavelength is plotted on …
the upper horizontal axis
in infrared radiation, the wavenumber is plotted on …
the lower horizontal axis
wavenumber (on the IR spectra) increases …
to the left
wavelength (on the IR spectra) increases …
to the right
frequency (v) is equal to …
c/λ
hc/λ is also equal to …
hcν̃
frequency (v) and wavenumber (ν̃) are …
directly proportional
the vertical axis of an IR spectra shows the …
percent transmittance (T)
percent transmittance (T) is equal to …
I (intensity of emerging light) / Io (intensity of light entering the sample)
if a sample absorbs all of the radiation …
the sample then has 0% transmittance
Absorbance (A) is the …
negative logarithm of transmittance
descriptions of IR peaks:
s = strong, w = weak, m = moderate, sh = sharp, br = broad
absoptions observed in an IR spectrum are the result of …
vibrations within a molecule
various oscillatory stretching and bending motions are called …
bond vibrations
a wave of electromagnetic radiation can transfer its energy to the vibrational wave motion of the C-H bond only …
if there is an exact match between frequency of the radiation and frequency of the vibration
if C-H vibration has a frequency of 9 × 10^13 s^-1 …
then it will absorb energy from radiation with the same frequency
when the radiation of a wavelength interacts with a vibrating bond …
energy is absorbed and the intensity of the bond vibration increases
after absorbing energy, bonds vibrate …
with the same frequency but with a larger amplitude
absorption of one photon of infrared radiation by a bond causes …
the vibrational energy to jump to the next energy level
the difference in energy needed to bring about the transition of vibrational energy from one level to the next is …
hvo, where vo is the vibrational frequency of the bond
the frequency of the photon that brings about the vibrational transition …
is the same as the frequency of the bond vibration
intense peak in the 1700 - 1750 region indicates …
the presence of carbonyl (C=O)
factors that govern the position of IR absorptions:
strength of the bond, masses of the atoms involved, type of vibration being observed
atoms connected by a stronger bond …
vibrate at a higher frequency
is takes more energy to …
stretch a tighter spring than a looser one
bond dissociation energy is the …
energy required to break a bond
the higher the bond dissociation energy …
the stronger the bond
the IR absorptions of stronger bonds (greater bond dissociation energies) occur …
at higher wavenumbers
the stretching frequency of stronger bonds are …
larger than weaker bonds
the vibration frequency of a bond between two atoms of different masses …
depends more on the mass of the lighter object
bending vibrations occur …
at lower frequencies (higher wavelengths) than stretching vibrations
bending vibrations are only possible …
when there are more than 2 atoms
a greater number of molecules in the sample and more absorbing groups within a molecule …
give a more intense spectrum
compounds rich in C-H bonds …
have stronger absorptions due to the C-H stretching vibrations
only the __________ is relevant to IR spectroscopy
vibrating electric field
polar chemical bonds …
have bond dipole moments
as the bond stretches …
the bond dipole increases (and vice versa)
bonds that do not have a dipole moment …
do not show up on the IR spectra (i.e internal alkenes)
molecular vibrations that occur but do not give rise to IR absorptions are …
said to be infrared-inactive
stretching absorptions of akyl C-H bonds are typically observed …
in the 2850 - 2960 region
the carbon-halogen stretching absorption of alkyl chlorides, bromides, and iodides …
appear in the low-wavenumber end of the spectrum
a single C-F bonds have a …
very strong stretching absorption in the 1000-1100 region
multiple flourines on the same carbon …
increase the stretching frequency
stretching vibration of the carbon-carbon double bond occurs …
in the 1640 - 1645 range
carbon-carbon double bonds have …
greater frequency of the absorption and smaller intensity
stretching absorptions of C-H bonds involving sp2 …
occur at wavenumbers greater than 3000
stretching absorptions of C-H bonds involving sp3 …
occurs at wavenumbers less than 3000
bonds to sp2 hybridized carbons …
are stronger, which means they vibrate at higher frequencies and greater wavenumbers
alkynes have C-C (triple bond) stretching absorption in …
the 2100-2200 region
O-H groups that are strongly hydrogen bonded give …
a broad peak between 3200 and 3400
in alcohols, there is a strong C-O stretching peak …
that occurs in the 1050 - 1200 region
primary alcohols absorb …
near the lower end of the 1050 - 1200 range (opposite for tertiary)
glass absorbs …
infrared radiation, and cannot be used in IR spec.
the conventional material used for IR spec. sample cells:
sodium chloride
the atom with the '“+” charge is considered the …
fragment ion
if a molecule contains only C,H, O and halogens, its even-electron fragment ions …
have odd mass
If a molecule contains only C, H, O, and halogens, its odd-electron fragment ions …
have even mass
If a molecule or odd-electron fragment ion contains an odd number of nitrogens …
it has an odd mass
an even-electron fragment with an odd number of …
nitrogens has even mass