functional groups

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

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

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
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?
has a higher molecular weight and more van der waals interactions
higher BP: hexane vs pentane?
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?
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
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?
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
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
particles of electromagnetic readiation
each photon has a discrete amount of energy
wavelength and frequency
electrommagnetic radiation can be characterized by its:
the distance form one point on a wave to the same point on an adjacent wave
the number of waves passing per unit of time, hertz
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
absorption of IR light causes changes in the vibrational motions of a molecule
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
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
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