Cyclohexanone exhibits its strongest IR peak at 5.86 mm, and at this wavelength
ID: 923020 • Letter: C
Question
Cyclohexanone exhibits its strongest IR peak at 5.86 mm, and at this wavelength a linear relationship exists between absorbance and concentration.
a. Identify the part of the molecule responsible for the absorbance at this wavelength.
b. Suggest a solvent that would be suitable for a quantitative analysis of cyclohexanone at this l.
c. A solution of cyclohexanone (2.0 mg/ml) in the solvent selected in part (b) exhibits an absorbance of 0.40, in a cell with a path length of 0.025 mm. What is the detection limit for this comp under these conditions if the noise associated with the spectrum of the solvent is 0.001 absorbance units?
Explanation / Answer
The information should be like the IR peak is 5.86 um, because 5.86 mm is not possible.
A. 5.86 um = 1706 cm^-1. This peak corresponds to the carbonyl group.
B. Any solvent miscible with cyclohexanone that doesn't have a carbonyl group will be a suitable solvent. Cyclohexane will work well for quantitative analysis of cyclohexanone.like chloroform, dichloromethane,etc.
C. It is related to Beer's law (A = a*b*c) since they give you absorbance (A), path length of the cell (b, convert to cm if needed), and concentration in g/mL (c, might have to convert to mol/L). Plugging in the values given, converted as needed, and solving for a (molar absorptivity) as follows will give you the answer.
0.401 = a * 0.0025 cm * (2 mg/mL)
a = 0.401 / 0.005 cm*mg/mL = 80.2 mL/(cm*mg) .
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