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## What is mass spectrometry (MS)?

Truong-Son N.
Featured 4 months ago

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):

• Inject liquid sample (might be a few $\mu L$ if you are injecting into a GC-MS setup; depends on the injection method)
• Vaporize sample (must be a gas to minimize undesirable fragmentation)
• Ionize sample (must be an ion to interact with electric/magnetic fields) to facilitate fragmentation
• Accelerate fragments into field (electric and/or magnetic) to separate ions by $\frac{m}{z}$ ratio
• Detect the ions to get a count for the abundance of each ion
• Acquire mass spectrum

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 ($> 3000 K$ or so), for example.

Some sort of ionization occurs (which facilitates fragmentation), such as:

• Chemical Ionization (soft/indirect ionization via the presence of ions in the system)
• Matrix-Assisted Laser-Desorption Ionization (a sample matrix is hit with a laser, ionized, and the matrix itself soft-ionizes the sample embedded within and shielded by the matrix)
• Electron "Impact", where an electron beam allows electrons to interact with the sample to knock off an electron and thus ionize it (hard ionization).

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, $m \text{/} z$. The ions then separate and then spiral towards some sort of collection surface that counts ions. This separation may be done with, for example, a quadrupole filter ("quadrupole" literally means "four [magnetic] poles").

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.

## How can you learn organic chemistry nomenclature?

Meave60
Featured 7 months ago

I would recommend using note cards.

#### Explanation:

First familiarize yourself with the rules of nomenclature for organic compounds.

Then draw the structural formula of a compound (I'm assuming you have been given a list) on one side of a note card, and the name on the other side, which is a tactile learning style.

Study them, look for the application of the rules to the names of the compounds. Then quiz yourself until you have them memorized. While studying, look for patterns, such as similarities and differences, which involves both a visual learning style and critical thinking.

You can also say the names orally, which will touch on the auditory learning style, and it's much easier to remember a word if you can pronounce it (even if your pronunciation is atypical).

My technique is to go through the cards and set aside the ones that I already know. Then I study the rest and add back the ones I already know. Then I go through all the cards again, and set aside the ones I got right (hopefully there will be more). Then I study the remaining cards, and add back the cards I already know. I keep doing this until I am able to get all of the names correctly from their structural formulas, and understand why they are named that way.

This will take some investment of your time, but it is a very useful studying tool and works for many different subjects.

## What is hybridization in organic chemistry?

Ernest Z.
Featured 5 months ago

Hybridization is the mixing of atomic orbitals to form new orbitals with different energies and shapes than the original orbitals.

#### Explanation:

Hybrid orbitals are mixtures of atomic orbitals in various proportions.

For example, the hybrid orbitals on the $\text{C}$ atom of methane consist of one-fourth $\text{s}$ character and three-fourths $\text{p}$ character.

We say they are ${\text{sp}}^{3}$ ("s-p-three") hybridized.

The four new hybridized orbitals have both $\text{s}$ and $\text{p}$ character.

The dumbbell shape reflects the $\text{p}$ character and (despite the picture) the big lobe is nearly spherical like an $\text{s}$ orbital.

The new orbitals all have the same energy but they point in different directions (towards the corners of a tetrahedron).

This leads to the most stable molecules when the $\text{C}$ atom forms bonds to four other atoms.

## How do dipole dipole forces arise?

Morgan
Featured 5 months ago

Dipole-dipole forces are intermolecular forces resulting from the attraction of the positive and negative ends of the dipole moments in polar molecules.

#### Explanation:

Dipole-dipole forces arise from the unequal distribution of electrons between atoms in a compound.

For example, consider $C {H}_{3} C l$. Chlorine is very electronegative, and so it pulls electrons away from the adjacent carbon atom toward itself, giving chlorine a partial negative charge and carbon a partial positive charge. We would refer to this molecule as polar because electrical charge is not symmetrically distributed.

A dipole moment ​is a measurement of the separation of the ends of a dipole, which are oppositely charged. Each molecular dipole moment has a positive and negative end.

Now, there is certainly more than one molecule of a compound in whatever substance you might be dealing with, which can be easy to forget. In a polar compound, the most stable arrangement has the positive end of one dipole close to the negative end of another. So in a solution of chloromethane, we would expect the molecules to orient in such a way that the partially negative-charged Cl of one molecule is aligned with the partially positive-charged C of another, and so on.

In summary, dipole-dipole forces are generally attractive intermolecular forces resulting from the attraction of the positive and negative ends of the dipole moments of polar molecules (1).

1. Wade, L. G.; Simek, J. W. In Organic Chemistry; Pearson: Glenview, IL, 2013; pp 60.

## What is the difference between an oxyacid and an organic acid? What are examples of each?

Dwight
Featured 2 months ago

The difference lies in the structure of the molecules and the manner in which the oxygen and hydrogen atoms are arranged. See below...

#### Explanation:

An oxyacid is one that will contain, in addition to hydrogen and another element (such as nitrogen, sulfur or phosphorus), a number of oxygen atoms.

Examples would include sulfuric acid ${H}_{2} S {O}_{4}$, and also sulfurous acid ${H}_{2} S {O}_{3}$, phosphoris acid ${H}_{3} P {O}_{4}$, nitric acid $H N {O}_{3}$ to name just a few.

An organic acid is one which contains, in its structure, the particular arrangement of atoms called a carboxyl group $- C O O H$

Examples include formic acid $H C O O H$, acetic acid (in vinegar) $C {H}_{3} C O O H$ and many more.

The difference comes in the actual structure of the molecule. In the oxyacid, the oxygen atoms are all bonded to the nitrogen or sulfur, or whatever it happens to be, with hydrogen atoms bonded to one or more of these oxygens.

In a carboxylic acid (the organic variety), a carbon is doubly bonded to one oxygen atom and singly bonded to a second oxygen. This second oxygen has the H atom bonded to it. So, a very particular structure.

"R" just represents the rest of the molecule.

## What is the mechanism for the hydrolysis of an anhydride into a carboxylic acid using HCl as a catalyst?

Truong-Son N.
Featured 1 month ago

This is a fairly standard mechanism (or mechanistic pattern) that you should get to know.

It is practically identical for anhydrides as it is for acyl halides (particularly acyl chlorides) and esters, and similar variations are seen in the acid-catalyzed hydrolysis of nitriles, amides, etc, wherein the electron-dense atom (e.g. $\text{O}$ in a carbonyl or $\text{N}$ in a nitrile) takes on a proton and becomes susceptible to nucleophilic attack.

It is perfectly acceptable to assume one starts with hydronium when a strong acid like $\text{HCl}$ is the acid catalyst.

1. The electron-dense carbonyl oxygen acquires a proton from the strong acid. Either carbonyl oxygen is fine, just not the ether oxygen.
2. Water then nucleophilically attacks the partially positive carbon, as oxygen withdraws electron density to break the carbonyl bond.
3. Proton transfer pt1.
4. Proton transfer pt2.
5. Tetrahedral collapse. You may choose which hydroxyl group does so, but it is usually the one that originated from the nucleophile that is typically used.
6. Regenerate the catalyst.

NOTE: You must replace ${R}_{1}$ and ${R}_{2}$ with $R$ groups that correspond to your specific substrate.

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