The correct answer is "Bombardment by free radical electrons which causes the formation of a radical cation and spontaneous bond cleavage throughout the molecule, depending on instability of the bond and stability of the fragments." First the parent molecule (the compound being identified) is bombarded by free radicals, resulting in a molecular radical cation, and then the molecular ion spontaneously fragments at the weak bonds and where the resulting fragments will be thermodynamically stable. These fragments then reach the detector plate at different places depending on the mass of each fragment.

Incorrect answers:

"Bombardment by free radical electrons which radicalizes the molecule at different atoms, resulting in distinct fragments" is incorrect because it indicates that the desired fragmentation of the molecule is through direct abstraction of a radical by the free radical, rather than a spontaneous self-cleaving process. If this occurs, it is not a desirable result, because the molecular ion will no longer be structurally in tact for the next chamber of the mass spectrometry in which it is meant to fragment and be separated based on mass/charge ratio. It is also somewhat sterically unlikely for a free radical electron to directly cause the splitting of carbon-carbon bonds in a sterically bulky organic molecule -- the free radical electron is more likely to abstract a proton and leave a positive radical charge on the molecule.

"Spontaneous homolytic cleavage of unstable bonds with good leaving groups, unmediated by electron bombardment" is incorrect because mass spectrometry methods use electrons to induce radical cation formation.

"Ionization through proton bombardment, depending on instability of the bond and stability of the fragments" is false because electrons, rather than protons, are used to ionize the molecule.

"Putting the molecule through a strong magnetic field, resulting in various electron spins of the hydrogens in the molecule" is incorrect because it does not reflect the spectra produced by mass spectrometry, nor the method by which molecular fragments are produced.

Constitutional isomers, also known as structural isomers, share the same molecular formula but have different bonding patterns, resulting in different orientations and branching. The given compound is a hydrocarbon, so constitutional isomers can only vary bonding and branching patterns; the functional groups cannot change. 1H NMR spectroscopy would show the configurations of neighboring hydrogens, and thereby indicate how the hydrogen and carbon atoms are connected in the different structures.

IR and Raman spectroscopy would indicate which functional groups are present, which would not be useful for hydrocarbons. The same applies for UV spectroscopy. Finally, mass spectrometry would give the mass of each structure, but would not be helpful since they would have the same molecular weight.

There are a couple of key functional group spectra that you must memorize. A carbonyl group will cause a sharp dip at about 1700cm-1, and an alcohol group will cause a broad dip around 3400cm-1.

3-pentanone contains ten hydrogens in total; however, 3-pentanone is a symmetric compound. The four hydrogens on the carbons next to the ketone have the same spin, and the six hydrogens on the methyl carbons have the same spin. The correct answer is two hydrogen peaks.

The molecule shown is completely symmetrical. This means that the hydrogens adjacent to the two carbons on the left of the ketone and the hydrogens adjacent to the carbons on the right of the ketone will have identical splitting patterns.

Let's focus on the right side. The farthest carbon has three hydrogens that will be split by two adjacent hydrogens. The carbon between the terminal methyl and the ketone has two hydrogens, split by three. On each side we will have two 3-hydrogen triplets and two 2-hydrogen quartets, totaling two unique and distinctive peaks composed of six and four hydrogens, respectively.

As an aside, in NMR readings, if the number of protons of each peak has a common denominator, it can likely be simplified. For example, a reading of this NMR might be reduced from a 6-H peak and 4-H peak, to a 3-H and 2-H peak, respectively. Do not get confused if the number of hydrogens in the reading does not match up to the number of hydrogens in the molecule; it just means it was most likely simplified.

Thin layer chromatography (TLC) is used to find the identity of a compound in a mixture. A TLC plate is a sheet of plastic or glass which is coated with a solid adsorbent, such as silica. A small portion of the mixture is spotted near the bottom of the TLC plate, which is placed in a liquid solvent so that the bottom of the plate is in the solvent. This liquid (solvent) slowly rises up the TLC plate by capillary action. As it moves past the spot that was applied to the plate, an equilibrium is formed for each portion of the mixture between the molecules of that portion which are adsorbed on the solid and the molecules which are still in solution. The components should differ in solubility and in the degree of their adsorption, and some components will travel further up the plate than others will. When the solvent reaches the top of the plate, the plate is removed from the liquid and the separated components of the mixture are seen, either with the naked eye or under UV light if components are not colored. Then, we can determine the identity of a component of the mixture using Rf value.

To find the Rf value, we divide the distance traveled by the unknown component by the distance traveled by the solvent front. This equation has nothing to do with the temperature, thickness of the adsorbent, or the amount of material spotted.

When dealing with peaks in NMR spectroscopy, remember that withdrawing groups on a molecule will push the proton signal farther to the left, or more downfield. Aldehydes have a distinctive peak at 9.5 ppm due to the effect of the oxygen atom in close proximity to the hydrogen.

The correct answer is -- this can be found by corroborating the molecular weight of with 100. It can also be found without looking at the multiple answer options, by knowing that in an alkane the ratio of carbon to hydrogen atoms will be . If is the number of carbon atoms in an alkane, and is the number of hydrogen atoms in an alkane, then the molecular weight of an alkane with carbon atoms is:

Since in this question the molecular weight is 100, as per the parent peak on the mass spec, the equation is:

Therefore, there are 7 carbon atoms and or 16 hydrogen atoms in this alkane. It's chemical formula is .

The correct answer is "." This part of the spectrum is totally unique for each distinct molecule, depending on its overall vibrational frequencies and stretching possibilities.

The carbonyl carbon of a carboxylic acid is always denoted carbon one of its chain. Molecules I and III each contain five carbons in their chain, which makes them pentanoic acids. Molecule IV is a butanoic acid but the chlorine substituents are present at carbons 2 and 3. Molecule II, the correct answer, is a carboxylic acid with a four-carbon chain and single chlorine atoms substituted at carbons 3 and 4.