An ester has a characteristic IR absorption at about 1750cm^-1. A saturated ketone has an absorption at about 1710cm^-1, while an unsaturated ketone has an absorption between 1650cm^-1 and 1700cm^-1. A nitrile has an IR frequency of about 2200cm^-1, while an alcohol has a strong, broad peak at about 3400cm^-1.

Carbonyl compounds all have peaks between roughly 1650cm^-1 and 1750cm^-1. Ketone peaks are generally observed at the lower end of this range, while aldehydes and esters are toward the higher end of the range.

Treating acetone, a secondary carbonyl, with a reducing agent, such as sodium borohydride (NaBH₄), will yield a secondary alcohol as the product.

When using IR spectroscopy, carbonyl (C=O) groups display characteristic peaks at approximately 1700cm^-1, while alcohol groups (O-H) display characteristic peaks around 3300cm^-1. The acetone would, therefore, initially have a characteristic peak at roughly 1700cm^-1. After the reduction reaction is complete, the resulting 2-propanol would display a characteristic peak roughly at 3300cm^-1.

The wavelength of 497nm corresponds to a blue-green color, however -carotene absorbs this wavelength. This means it reflects the complementary color on the opposite end of the color spectrum. This gives -carotene a red-orange appearance, as only the reflected wavelengths will be returned to the eye.

It is important to memorize a couple key functional groups, and where they are located on an IR spectrum. If you see a sharp peak near 1700cm^-1, you can assume it is made by a carbonyl group. 

Similarly, a wide peak around 3000cm^-1 will be made by a hydroxyl group.

The wavelength of light absorbed by a pigment is related to the number of conjugated double bonds in the molecule. The eye will begin to perceive color when the number of conjugated double bonds in a molecule becomes around eight. At this point, the color yellow can be perceived by the eye. In order for -carotene to give carrots a more yellowish color, it must have a change in the number of conjugated double bonds so that the pigment absorbs a shorter wavelength of light. This way, it will emit complementary light with a wavelength closer to yellow on the visible spectrum.

RNA and DNA are hydrophilic substances, and will be found in the aqueous layer after the cells are lysed. Based on molecular weights of water (18), phenol (94), and chloroform (119), it is evident that the aqueous layer will be on the top, denoted as layer 1.

Lipids and other cellular debris are hydrophobic, and can be dissolved in the organic (bottom) layer. We know that the organic solvents will settle in layer 3 due to their relative densities compared to water. Phenol and chloroform are heavier molecules than water, with molecular weights of 94 and 119 respectively, and will thus be found in the bottom layer.

The purpose of a phenol:chloroform extraction is to separate organic and aqueous cellular components. The lysis buffer is an aqueous solution, while the phenol:chloroform extraction solution is organic. Generally, organic solutions are more dense that aqueous solutions, resulting in the aqueous solution being on the top and organic being on the bottom. The interphase consists of proteins containing both hydrophilic and hydrophobic domains.

You can also determine relative density by calculating the molecular weights of the solvents. Doing so will show that water (MW = 18) is much lighter than phenol (MW = 94) or chloroform (MW = 119).

Proteins generally contain both hydrophobic and hydrophilic domains, and therefore, do not completely associate with either the organic or aqueous layers. They can be found in the interphase layer, denoted as layer 2. This allows different domains of the protein to interact with each phase. Hydrophilic regions will interact with the aqueous phase (layer 1), while hydrophobic regions will orient toward the organic phase (layer 3).

After the first extraction, the DNA will be found in the aqueous phase due to its negative charge and hydrophilic nature. Transferring the aqueous phase (with DNA) and adding ethanol and salt will not result in an extraction; there will only be one phase after centrifugation: the aqueous phase. Following centrifugation, the DNA and salt precipitate from the aqueous ethanol solution and form a DNA pellet.