Exam 1 Flashcards
Modern technique for structure of organic compounds: Mass Spectrometry
What is the size and formula of the compound?
Modern technique for structure of organic compounds: Infrared Spectroscopy
What functional groups are present in the compound?
Modern technique for structure of organic compounds: Ultraviolet spectroscopy
Is a conjugated pi electron system present in the compound?
Modern technique for structure of organic compounds: Nuclear magnetic resonance spectroscopy
What is the carbon-hydrogen framework of the compound?
Spectroscopy involves an interaction between
matter and light (electromagnetic radiation)
Photos
Waves of energy or packets (particles) of energy
Properties of light waves:
Wavelength and frequency
Wavelength is _____ proportional to energy
inversely
Frequency is ____ proportional to energy
directly
Electromagnetic radiation exhibits dual behavior:
Particle-like (photon) and wave-like
Wavelength (λ)
Distance from one wave maximum to the next
Frequency (v)
Number of waves that pass by a fixed point per unit time (measured in hertz)
Amplitude
Height of a wave measured from midpoint to peak
Electromagnetic spectrum
Range of possible frequencies of light
NMR region of electromagnetic spectrum
Radio waves
NMR info obtained
Specific arrangement of all carbon and hydrogen atoms in the compound
IR Region of Electromagnetic Spectrum
Infrared
IR Information Obtained
Functional groups present in the compound
UV-VIS Region of Electromagnetic Spectrum
Visible and ultraviolet
UV-VIS spectroscopy info obtained
Any conjugated π system present in the compound
On the macroscopic scale, matters appears to exhibit
continuous behavior rather than quantum behavior
Matter exhibits _____ like properties and ______ like properties
Particle and wave
Matter on the molecular scale exhibits quantum behavior
A molecule will only rotate or vibrate at certain rates (energies)
For the electrons in covalent bonds, vibrational energies are separated by
gaps (quantized)
If a photon of light strikes the molecule with the exact amount of energy needed, the light is
absorbed and vibrational excitation will occur
IR light generally causes
molecular vibration. Different types of bonds absorb different IR energies
Molecular bonds can vibrate by
stretching or by bending in a number of ways
An IR spectrophotometer irradiates a sample with
all frequencies of IR light
Frequencies absorbed by IR sample tells us the
types of bonds (functional groups) that are present
IR samples are deposited on a
salt plate which are transparent to IR radiation or can be dissolved in a solvent or in a KBr pellet
IR absorption spectrum plots the % transmittance as a
function of frequency. The “peaks” are called absorption bands
Units of frequency in IR are called
Wavenumbers. Values range from 400 to 4000 cm^−1
A signal (peak) on the IR spectrum has three important characteristics
Wavenumber, intensity, and shape
The frequency (wavenumber) for a stretching vibration depends on
bond strength and mass difference of the atoms bonded together.
The stronger the bond, the ____ stretching frequency
higher
The larger the mass difference, the ____ stretching frequency
higher
X-H wavenumber
4000 - 2700 cm^-1
C triple bonded to C wavenumber
2300 - 2100 cm^-1
C triple bonded to N wavenumber
2300 - 2100 cm^-1
C=C wavenumber
1850 - 1600 cm^-1
C=N wavenumber
1850 - 1600 cm^-1
C=O wavenumber
1850 - 1600 cm^-1
C-C wavenumber
1600 - 400 cm^-1
C-N wavenumber
1600 - 400 cm^-1
C-O wavenumber
1600 - 400 cm^-1
Region above 1500 cm^-1 in IR is called the
diagnostic region and the peaks in this region provide clear information
The region below 1500 cm^-1 is called the
fingerprint region. There are many signals here and it is difficult to analyze
The higher the s character of the carbon, the stronger the C-H bond, and so the ____ the stretching frequency of the C-H bond
higher
Alkyl C-H bonds come just ____ 3000 cm^-1
under
Alkenyl and Alkynyl C-H bonds are ____ 3000 cm^-1
over
Resonance delocalization of electrons affects the strength of a covalent bond and thus the
wavenumber of a stretching signal
The more delocalized the p electrons, the weaker the p bond, and the
lower the stretching frequency
Conjugated carbonyls have
lower stretching frequencies
When a bond undergoes a stretching vibration, its dipole moment
oscillated
Formula for dipole moment includes the
distance btwn the partial charges
Oscillating dipole moment creates an
electric field surrounding the bond
The more polar the bond, the greater the opportunity for
interaction btwn the waves of the electrical field and the IR radiation
Greater bond polarity =
stronger IR signals
If a bond is completely symmetrical, then a stretching frequency (is or is not) observed in the IR spectrum
is not
Primary and secondary amines exhibit
N-H stretching signals
secondary amines exhibit only ___ signal(s) for N-H bonds
1
primary amines exhibit ____ signal(s) for the N-H bonds
two
Symmetric stretching
Stretching in the same direction
Asymmetric stretching
Stretching in opposite directions
IR Spectrum: 1600-1850 cm^-2, check for
double bonds
IR Spectrum: 2100-2300 cm^-2, check for
triple bonds
IR Spectrum: 2700-4000 cm^-2, check for
X-H Bonds
Mass spec can be used to identify compounds and help with
pharmaceutical, biotech, clinical, environmental, geological, forenscis, and many more
Mass spec (MS) measured the
mass and molecular weight of a molecule
Mass spec provides structural info by finding the
masses of fragments produced when molecules break apart
Mass spec is used to determine the molar mass and ____ of a compound
formula
In a mass spec, a compound is
vaporized, ionized, and undergoes fragmentation. the masses of ions are detected and graphed
Most common method of ionizing molecules is by
Electron impact where the sample is bombarded with a beam of high energy electrons that causes an electron to be ejected from the molecule
Mass of _____ is the same as the parent compound (mass of an electron is negligible)
radical cation
If the radical cation remains intact, it is known as the
molecular ion (M+•) or parent ion
Most of the radical ions in a mass spec are fragmented into a radical and a cation. The ions are deflected by a magnetic field and their _____ is detected
mass to charge ratio (m/z). Neutrally charged fragments are not detected
Mass spec shows relative abundance of each
cation that was detected
In mass spec, base peak is the
tallest peak in the spectrum and is the most abundant fragment
In mass spec, peaks above molecular weight appear as a result of
naturally occurring heavier isotopes in the sample
In mass spec, molecular weight is determined from
molecular ion peak
In mass spec, if parent ion isn’t present, it’s due to
electron bombardment causing breakdown, “softer” methods such as chemical ionization are used
M+1 peak results from presence of
13C and 1H
Fragmentation occurs when
high-energy cation radical falls apart (1 fragment retains + charge and is a carbocation, and 1 fragment is a neutral radical fragment)
1st step in analyzing a mass spec is to identify
M+• peak
M/z of parent ion in mass spec equals
molar mass of compound
Odd-massed M+• peaks means there is an
odd number of N atoms in the molecule
An even-massed M+• peak generally indicates an
absence of Nitrogen, or an even number of N atoms present
1% of all carbon atoms are
13C
More carbon atoms in a compound, more abundant _____ peak is in mass spec
(M+1)+•
Tertiary is (more or less) stable than primary or secondary
more
Alcohols undergo two types of fragmentation
alpha cleavage and dehydration
Ketones and aldehydes also undergo alpha cleavage of bond btwn
carbonyl group and neighboring carbon
Amines undergo ____ fragmentation
alpha cleavage
Carbonyls undergo ____ fragmentation
McLafferty rearrangement
Common fragments in mass spec: M-15
Loss of methyl radical
Common fragments in mass spec: M-29
Loss of ethyl radical
Common fragments in mass spec: M-43
Loss of propyl radical
Common fragments in mass spec: M-57
Loss of butyl radical
Common fragments in mass spec: M-18
Loss of water (from an alcohol)
Common fragments in mass spec: M-X (where X is an even number)
McLafferty rearrangement (Ketone or aldehyde)
For degrees of unsaturation, alkanes, or unsaturated hydrocarbons, follow the formula
CnH2n+2
Degree of unsaturation
A pi bond or a ring. For every DU in a compound in a compound, the number of Hs is reduced by 2. These are unsaturated compounds
1 degree of unsaturation equals
1 unit on the hydrogen deficiency index (HDI)
For HDI, a halogen is treated as if it were a
hydrogen atom
For HDI, an oxygen (does or does not) affect HDI
does not
For HDI, a nitrogen (increases or decreases) the number of expected hydrogens by one
increases
Use this formula to calculate HDI
HDI = 1/2 (2C + 2 + N - H - X)
If HDI = 0, molecule (does or does not) have any rings, double bonds, or triple bonds
does not
General formula for Calculating DU and/or HDI
(Number of Carbons) - (Number of Hydrogens / 2) - (Number of Halogens / 2) + (Number of Nitrogens / 2) + 1
Nuclear magnetic resonance (NMR) spec may be most powerful method of
gaining structural info about organic compounds
NMR involves an interaction btwn
electromagnetic radiation (light) and the nucleus of an atom
Magnetic moment exists perpendicular to
axis of nuclear spin
Beta spin state
Opposing B0, higher energy spin state
alpha spin state
Aligned with B0, lower energy spin state
The more shielded a nucleus is with electron density, the
smaller the alpha beta energy gap
Pulsed Fourier transform spectrometer
Brief pulse of radio energy (all relevant wavelengths) is used to excite the sample
In NMR, position of peaks tells us
about the electronic environment of each kind of H in the compound
In NMR, the number of signals (peaks) tells us about
the different kinds of hydrogens (protons) that are present in the molecule
In NMR, the peak area (integration) tells us about the
number of hydrogens (protons) represented by each peak
In NMR, signal spitting (splitting patters) tells us about the
information about neighboring hydrogens
Homotopic
Two H’s that are in identical environments and have the same NMR signal
Number of signals in a NMR spec indicates the
number of different kinds of protons in a compound
Homotopic protons
If the molecule has an axis of rotational symmetry that allows one proton to be rotated onto the other without changing the molecule
Enantiotopic protons
If the molecule has a plane of reflection that makes one proton the mirror image of the other
Diastereotopic
Compounds that are not chemically equivalent
2 protons on a CH2 group will be equivalent if there are
no chiral centers in the molecule
2 protons on a CH2 group will not be equivalent if there is
a chiral center in the molecule
Downfield has (high or low) field strength
low
Upfield has (high or low) field stregth
high
Shielded protons require a ____ external magnetic field to be excited at the same energy as deshielded protons
stronger. They have smaller energy gaps and absorb lower energy wadio raves
Deshielded protons are in the ____ area
downfield
Shielded protons are in the ____ area
upfield
Diamagnetic anisotropy
Different regions of localized space have different magnetic strengths
Integration (area) under peak quantifies the
relative number of protons giving rise to a signal
J value (coupling constant)
Distance between peaks of a splitting pattern measured in units of Hz
Carbon - 13
Only carbon isotope with a nuclear spin. Natural abundance is 1.1%
In 13C NMR spec, each type of Carbon produces
one signal or peak. There is no C-C coupling that causes signal splitting
Proton decoupled spectrum
Signals for each carbon are singlets (no 13C-H splitting is shown)
Proton coupled spectrum
Each different carbon is splitted by H bonded to it; n+1 rule for 13C-H splitting where n=# of H bonded to carbon in question. Signal for each C has n+1 peak
Chemical shift for 13C NMR
Chemical shifts occur btwn 0 and 220 ppm
In 13C NMR, sp3 signal is at
0 to 9 wavelength
In 14 C NMR, sp2 C is at
110 to 220 wavelength
In 13C NMR, C(=O) is at
low field, 160 to 220 wavelength
In 13 C NMR, summary (does/does not) affect number of signals
does
MRI (magnetic resonance imaging) instruments are essentially
1H NMR specs
Vibrating bonds can be demoted to a lower vibration state by
emitting IR radiation. Ex; night vision goggle or mammograms
Blood can be analyzed with
Mass spec bc it can be used to detect abnormal blood levels of amino acids, fatty acids, and sugars
Drug purity can be determined with
mass spectrometry. can measure blood or urine levels for it
Bacterial infection and specific protein biomarkers for cancer can be detected with
mass spec.
Microwaves are a direct application of quantum mechanics and spectroscopy dues to the fact that it
causes rotational excitement
Impurities of Heparin Sodium can be detected with
NMR
