Specific Rotation of Enantiomer of 2-Butanol

Specific rotation is a measure of the extent to which a compound rotates plane-polarized light. It is a characteristic property of chiral compounds, which have non-superimposable mirror images (enantiomers). The specific rotation of a compound is represented by the symbol [α].

To determine the specific rotation of an enantiomer of 2-butanol, we need to use the observed rotation and the concentration of the solution.

Observed Rotation
The observed rotation is given as 4.05 counter clockwise. This means that the plane of polarized light is rotated by 4.05 degrees in the counter-clockwise direction when it passes through the solution of the enantiomer of 2-butanol.

Concentration of the Solution
To calculate the specific rotation, we need to know the concentration of the solution. The solution was prepared by diluting 6g of 2-butanol to a total volume of 40ml. Therefore, the concentration can be calculated using the formula:

Concentration (g/ml) = Mass of solute (g) / Volume of solution (ml)

Concentration = 6g / 40ml
Concentration = 0.15 g/ml

Specific Rotation Calculation
The specific rotation of a compound is given by the formula:

[α] = observed rotation / (concentration * length of the polarimeter tube)

In this case, the length of the polarimeter tube is given as 200 mm, which is equivalent to 20 cm.

[α] = 4.05 / (0.15 * 20)
[α] = 4.05 / 3
[α] = 1.35

Therefore, the specific rotation of the enantiomer of 2-butanol is 1.35.

Explanation
The observed rotation of 4.05 counter clockwise indicates that the enantiomer of 2-butanol rotates the plane of polarized light in the counter-clockwise direction. The specific rotation value of 1.35 indicates that the enantiomer of 2-butanol has a slight optical activity.

The specific rotation is influenced by factors such as the concentration of the solution and the length of the polarimeter tube. In this case, the concentration of the solution was calculated to be 0.15 g/ml, and the length of the polarimeter tube was 20 cm. These values were used to calculate the specific rotation using the formula [α] = observed rotation / (concentration * length of the polarimeter tube).

By determining the specific rotation, we can characterize the optical activity of the enantiomer of 2-butanol and distinguish it from its mirror image, which would have the opposite specific rotation. The specific rotation is an important property used in the identification and characterization of chiral compounds.