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Mass Spectroscopy (MS), in the most basic sense, is for tracing the fragmentation patterns of molecular ions in order to identify them. This tends to be more useful when coupled with other processes, such as Gas Chromatography and Liquid Chromatography.
MS has an interesting process by which we do the following (in a vacuum):
This is the essential process of Mass Spectroscopy.
In further depth:
Inject the sample via some method, such as the 30-ft long tube you use in Gas Chromatography (i.e. the GC is interfaced with MS and you have a GC-MS setup), for example.
Some sort of sample vaporization occurs so that you have a gaseous sample. This may be done with, perhaps, a coil with electric current flowing through it, or maybe a hot flame (
Some sort of ionization occurs (which facilitates fragmentation), such as:
The point of having both soft and hard ionization is that soft ionization better-retains the parent peak during fragmentation, so that you can find the peak that corresponds to the molecular mass of the original ion.
The fragments are then accelerated into an electric and/or magnetic field for the purpose of separating it by a mass-to-charge ratio,
The ions must reach a detector, such as a Faraday Plate or Faraday Cup. Behind it would be some sort of transducer to convert/encode the number of ions that are counted into a current that acts as a signal for a computer to read, so that it can generate some sort of display to give you your mass spectrum.
Atoms achieve stability in a single covalent bond by sharing valence electrons to create filled electron shells which are stable.
"Co-" means to share. Valence electrons are the outermost electrons in an atom. By sharing the valence electrons, atoms can achieve a filled valence shell which is stable.
The oxygen in turn shares one of its valence electrons with each of the two hydrogens in
#\mathbf("H"_2"O")#(water), providing each hydrogen with a filled shell. By sharing all the atoms are filled and "happy", like neon and helium.
π bonds are formed because the side-by-side overlap of
Consider the formation of ethylene,
This leaves an unhybridized p orbital containing one electron on each
When you have two
We call this a π bond.
It forms because the π electrons are as close as they can get to the two nuclei and are therefore in their lowest energy state.
A π bond can only form only after a σ bond has already formed. It is always part of a double or triple bond.
They form due to the movement and attractions of electrons in atoms and molecules.
A dipole is the separation of two opposite charges, or, in this case, partial charges.
To answer your question, we have to distinguish between the different types of dipoles. There are three different types of dipole:
Permanent dipoles exist in molecules with covalent bonding where one atom is more electronegative than the other. The atom which is more electronegative attracts the bonded pair of electrons to it, increasing its electron density. It thus becomes slightly negative (
Oscillating dipoles occur by chance due to the random movement of electrons in atoms. At any point, the electrons in an atom can all be concentrated on one end, reducing the electron density of the other. This causes one end of the atom to become
Induced dipoles form when a molecule with a permanent or oscillating dipole approaches a non-polar molecule (or the other way around). As the non-polar molecule approaches the polar one, its electrons will be attracted to the
This sort of dipole can also form when a non-polar molecule approaches an ionic molecule.
The three factors that determine carbocation stability are adjacent (1) multiple bonds; (2) lone pairs; and (3) carbon atoms.
(1) Adjacent multiple bonds
An adjacent π bond allows the positive charge to be delocalized by resonance.
Resonance delocalization of the charge through a larger π cloud makes the cation more stable.
(2) Adjacent lone pairs
A lone pair on an adjacent atom stabilizes a carbocation.
The cation is more stable because the charge is spread over two atoms.
(3) Adjacent carbon atoms
The stability of carbocations increases as we add more carbon atoms to the cationic carbon.
The stabilization is explained by a type of resonance called hyperconjugation.
The delocalization of charge stabilizes the carbocation.
Thus, the more alkyl groups there are surrounding the cationic carbon, the more stable it becomes.
That gives us the order of stability:
Here's how I would do it.
These are the reaction conditions for generating benzyne intermediates.
The reaction of ortho-bromoanisole with potassium amide in liquid ammonia (b. p. -33 °C) is extremely rapid.
Step 1. The amide ion attacks the
Step 2. Loss of
The elimination is by an E2cb pathway.
Step 3. Addition of
The strain caused by a triple bond in a benzene ring can be relieved by a nucleophilic addition (
The methoxy group is electron-withdrawing by induction, so the nucleophile will attack
Step 4. Protonation of the carbanion.
The product is meta-methoxyaniline.
The reaction with para-bromoanisole also follows a benzyne mechanism.
The nucleophile can attack either end of the triple bond, and the methoxy group is far enough away that its inductive effects are minimal.
The product is a mixture of para- and meta-methoxyaniline.
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