functional groups

Alkyl, and occasionally aryl (aromatic) functions are represented by the R-

Methyl: CH3–
Ethyl: CH3CH2–
Propyl: CH3CH2CH2–
Isopropyl: (CH3)2CH–
Phenyl: C6H5–
etc.

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Br : MS
M+2 peak is nearly as tall as m peak
Cl : MS
M+2 peak is 1/3 of the size of M+ peak
N : MS
has an odd # for their M+ peaks
IR: high energy
high frequency
large wave#
short wave lengths
intensity of bond
greater the charge in the dipole moment, more intense the absorption
-more polar the bond, the more intense it is
IR characteristics
-cant determine structure alone
-some signals are ambiguous
-if there is an absence of a signal, thats definite proof that the function roups is absent
-look at the literature value of the compound to confirm or vice versa
triplanar: degrees?
120 degress
linear: bond angle?
109.5 degrees
linear: bond angle?
180 degrees
C-C :bond length?
1.54 A
C=C: bond length?
1.34 A
C=-C: bond length?
1.20 A
condensed formula
CH3OCH3
acid strength: down group
larger size differnce, weaker bond
acid strength: across row
greater electronegativity, more polorized bond
acid strength: c-H vs C-O
conjugate base is stablized by inductive and resonance effects
acid strength: molecular weight
conjugate base is better stablized by inductive effects
stronger bases than -OH put in water
leveling effect
-bases stronger than OH- will simply deprotonate water to form the weaker base OH-
molecular weight
what is the main piece of information sought from analysis of a compound by low-resolution mass spectrometry?
molecular formula
What is the main piece of information sought from analysis of a compound by high resolution mass spectometry?
identification of functional groups
What is the main piece of information sought form analysis of a compound by infrared spectroscopy?
-hexane
has a higher molecular weight and more van der waals interactions
higher BP: hexane vs pentane?
-alcohol
can hydrogen bond to its neighbors
higher BP: ether vs alcohol
1. ion charges
2. higher molecular weight
3. has halogen
most soluable in water?
-more symmetrical
most inportant factor for higher MP?
1. ion-ion, coulombic attraction
2. dipole-dipole attraction
3. hydrogen bond – typeof dipole-dipole
4. van der waals -transient dipole-dipole
explain 4 differnt types of bonds
a gas chromotograph and a mass spectrometer
what two instruments are coupled together in a so-called GC-MS?
compounds with ane ven # of nitrogenn
(or O) have an even molecular mass
compounds with an odd # of nitrogems have an odd molecular mass
explain what the nitrogen rule is
the stretch produces no charge in the dipole moment
why cant the symmetrical stretch of carbon dioxide produce a peak (absorption) in a normal IR spectrum?
H2O
has a greater propensity to donate a proton because the conjugate base (OH-) would be more stable than (NH2-) due to the more electronegative oxygen atom
which one is the stronger acid and why?
H2O vs NH3
CH3CF2COOH
has a greater propensity to donate a proton because the conjugate base is more stable as a result of the more effective (-) charge delocalization due to stronger induction thru the sigma bonds by the more proximal F atoms
which one is the stronger acid?
F2CHCH2COOH vs CH3CF2COOH
HCl
has a greater propensity to donate a proton becaus the conjugate base (Cl-) would be more stable than (F-) due to Cl- being larger and the negative charge being dispersed over a larger volume
which one is the stronger acid?
HF vs HCl
CH=-CH
has agreater propensity to donate a proton because the conjugate base is more stable as a result of the lone pair residing in an sp orbital (as opposed to an sp3 orbital) which has more s character (50%), so the lone pair is in a lower energy, closer to the nucleus
which is the stronger acid?
CH3CH3 vs CH=-CH
pie bonds and heteroatoms
in general, what are two structural features in organic compounds, any one of which, that give rise to so-called functional groups and useful reactivity?
electromagnetic radiation
radient energy having dual properties of both waves anad particles
photons
particles of electromagnetic readiation
quantum
each photon has a discrete amount of energy
wavelength and frequency
electrommagnetic radiation can be characterized by its:
wavelength
the distance form one point on a wave to the same point on an adjacent wave
frequency
the number of waves passing per unit of time, hertz
true
t/F?
for absorption ot occur, the energy of the photon must match the difference between two energy states in a molecule
IR radiation
the energy source used in IR spectroscopy
true
t/f?
absorption of IR light causes changes in the vibrational motions of a molecule
true
t/f?
IR spectroscopy distinguishes between the different kinds of bonds in a molecule, so it is possible to determine the functional groups present
1. light passes through a sample
3. frequencies that match the vibrational frequencies are absorbed,and the remaining light is transmitted to a detector
3. an “IR spectrum is a plot of the amount of transmitted light versus its wavenumber
characteristics of IR:
100% transmittance
that all the light shone on a sample is transmitted and none is absorbed
0% transmittance
that none of the light shone on the sample is transmitted and all is absorbed
true
t/f?
stronger bonds vibrate at a higher frequency, so they absorb at higher wavenumbers
.
bonds with lighter atoms vibrate at higher frequency, so they absorb at higher wavenumbers
.
the higher the percent s-character, the stronger the bond and the hgiher the wavenumber of absorption
.
for a bond to absorb in the IR, there must be a change in dipole moment during the vibration
IR inactive
symmetrical nonpolar bonds do not absorb in the IR
.
IR spectroscopy is often used to determine the outcome of a chemical reaction
.
i a mass spectrometer, a molecule is vaporized and ionized by bombardment with a beam ofhigh-energy electrons
.
the electron beam ionizes the molecule by causing it to eject an electron
radical cation, M+
when the elctron beam is ionized the molecule, the species that is formed is called?
.
the mass of M+ represents the molecular weight of M
.
because M is unstable, it decomposes to fomr fragments of radicaals and cations that have a lower molecular weight than M+
.
the mass spectrum analyzes the masses of cations, a plot of the amount of each cation versus its mass to charge ratio
.
when the sample is injected into the GC, it is vaporized and swept by an inert gas through the column and components are usually seperated by boiling points
x

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