# 5.3: Optical Activity (2023)

1. Last updated
2. Save as PDF

Objectives

After completing this section, you should be able to

1. describe the nature of plane-polarized light.
2. describe the features and operation of a simple polarimeter.
3. calculate the specific rotation of a compound, given the relevant experimental data.
##### Key Terms

Make certain that you can define, and use in context, the key terms below.

• analyzer
• dextrorotatory
• levorotatory
• optically active
• plane-polarized light
• polarimeter
• polarizer
• specific rotation, $\ce{\sf{[\alpha]_{D}}}$
##### Study Notes

A polarizer is a device through which only light waves oscillating in a single plane may pass. A polarimeter is an instrument used to determine the angle through which plane-polarized light has been rotated by a given sample. You will have the opportunity to use a polarimeter in the laboratory component of the course. An analyzer is the component of a polarimeter that allows the angle of rotation of plane-polarized light to be determined.

Specific rotations are normally measured at 20°C, and this property may be indicated by the symbol $\ce{\sf{[\alpha]^20_{D}}}$. Sometimes the solvent is specified in parentheses behind the specific rotation value, for example,

$\ce{\sf{[\alpha]^20_{D} = +12}}$° (chloroform)

For liquids, the specific rotation may be obtained using the neat liquid rather than a solution; in such cases the formula is

$[ α ] D temp (neat)= α l×d$

where α is the observed rotation, l is the path length of the cell (measured in decimetres, dm), and d is the density of the liquid.

Identifying and distinguishing enantiomers is inherently difficult, since their physical and chemical properties are largely identical. Fortunately, a nearly two hundred year old discovery by the French physicist Jean-Baptiste Biot has made this task much easier. This discovery disclosed that the right- and left-handed enantiomers of a chiral compound perturb plane-polarized light in opposite ways. This perturbation is unique to chiral molecules, and has been termed optical activity.

## Polarimetry

Plane-polarized light is created by passing ordinary light through a polarizing device, which may be as simple as a lens taken from polarizing sun-glasses. Such devices transmit selectively only that component of a light beam having electrical and magnetic field vectors oscillating in a single plane. The plane of polarization can be determined by an instrument called a polarimeter, shown in the diagram below.

Operating principle of an optical polarimeter.
1. Light source 2. Unpolarized light 3. Linear polarizer 4. Linearly polarized light
5. Sample tube containing molecules under study 6. Optical rotation due to molecules
7. Rotatable linear analyzer 8. Detector
Image credit: Wikipedia

Monochromatic (single wavelength) light, is polarized by a fixed polarizer next to the light source. A sample cell holder is located in line with the light beam, followed by a movable polarizer (the analyzer) and an eyepiece through which the light intensity can be observed. In modern instruments an electronic light detector takes the place of the human eye. In the absence of a sample, the light intensity at the detector is at a maximum when the second (movable) polarizer is set parallel to the first polarizer (α = 0º). If the analyzer is turned 90º to the plane of initial polarization, all the light will be blocked from reaching the detector.

Chemists use polarimeters to investigate the influence of compounds (in the sample cell) on plane polarized light. Samples composed only of achiral molecules (e.g. water or hexane), have no effect on the polarized light beam. However, if a single enantiomer is examined (all sample molecules being right-handed, or all being left-handed), the plane of polarization is rotated in either a clockwise (positive) or counter-clockwise (negative) direction, and the analyzer must be turned an appropriate matching angle, α, if full light intensity is to reach the detector. In the above illustration, the sample has rotated the polarization plane clockwise by +90º, and the analyzer has been turned this amount to permit maximum light transmission.

The observed rotations ($$\alpha$$) of enantiomers are opposite in direction. One enantiomer will rotate polarized light in a clockwise direction, termed dextrorotatory or (+), and its mirror-image partner in a counter-clockwise manner, termed levorotatory or (–). The prefixes dextro and levo come from the Latin dexter, meaning right, and laevus, for left, and are abbreviated d and l respectively. If equal quantities of each enantiomer are examined , using the same sample cell, then the magnitude of the rotations will be the same, with one being positive and the other negative. To be absolutely certain whether an observed rotation is positive or negative it is often necessary to make a second measurement using a different amount or concentration of the sample. In the above illustration, for example, α might be –90º or +270º rather than +90º. If the sample concentration is reduced by 10%, then the positive rotation would change to +81º (or +243º) while the negative rotation would change to –81º, and the correct α would be identified unambiguously.

(Video) 5.3-Optical Activity

Since it is not always possible to obtain or use samples of exactly the same size, the observed rotation is usually corrected to compensate for variations in sample quantity and cell length. Thus it is common practice to convert the observed rotation, α, to a specific rotation, by the following formula:

$[\alpha]_D = \dfrac{\alpha}{l c} \tag{5.3.1}$

where

• $$[\alpha]_D$$ is the specific rotation
• $$l$$ is the cell length in dm
• $$c$$ is the concentration in g/ml
• $$D$$ designates that the light used is the 589 line from a sodium lamp

Compounds that rotate the plane of polarized light are termed optically active. Each enantiomer of a stereoisomeric pair is optically active and has an equal but opposite-in-sign specific rotation. Specific rotations are useful in that they are experimentally determined constants that characterize and identify pure enantiomers. For example, the lactic acid and carvone enantiomers discussed earlier have the following specific rotations.

 Carvone from caraway: [α]D = +62.5º this isomer may be referred to as (+)-carvone or d-carvone Carvone from spearmint: [α]D = –62.5º this isomer may be referred to as (–)-carvone or l-carvone Lactic acid from muscle tissue: [α]D = +2.5º this isomer may be referred to as (+)-lactic acid or d-lactic acid Lactic acid from sour milk: [α]D = –2.5º this isomer may be referred to as (–)-lactic acid or l-lactic acid

A 50:50 mixture of enantiomers has no observable optical activity. Such mixtures are called racemates or racemic modifications, and are designated (±). When chiral compounds are created from achiral compounds, the products are racemic unless a single enantiomer of a chiral co-reactant or catalyst is involved in the reaction. The addition of HBr to either cis- or trans-2-butene is an example of racemic product formation (the chiral center is colored red in the following equation).

 CH3CH=CHCH3 + HBr (±) CH3CH2CHBrCH3

Chiral organic compounds isolated from living organisms are usually optically active, indicating that one of the enantiomers predominates (often it is the only isomer present). This is a result of the action of chiral catalysts we call enzymes, and reflects the inherently chiral nature of life itself. Chiral synthetic compounds, on the other hand, are commonly racemates, unless they have been prepared from enantiomerically pure starting materials.

There are two ways in which the condition of a chiral substance may be changed:
1. A racemate may be separated into its component enantiomers. This process is called resolution.
2. A pure enantiomer may be transformed into its racemate. This process is called racemization.

## Enantiomeric Excess

The "optical purity" is a comparison of the optical rotation of a pure sample of unknown stereochemistry versus the optical rotation of a sample of pure enantiomer. It is expressed as a percentage. If the sample only rotates plane-polarized light half as much as expected, the optical purity is 50%.

Because R and S enantiomers have equal but opposite optical activity, it naturally follows that a 50:50 racemic mixture of two enantiomers will have no observable optical activity. If we know the specific rotation for a chiral molecule, however, we can easily calculate the ratio of enantiomers present in a mixture of two enantiomers, based on its measured optical activity. When a mixture contains more of one enantiomer than the other, chemists often use the concept of enantiomeric excess (ee) to quantify the difference. Enantiomeric excess can be expressed as:

For example, a mixture containing 60% R enantiomer (and 40% S enantiomer) has a 20% enantiomeric excess of R: ((60-50) x 100) / 50 = 20 %.

##### Exercise $$\PageIndex{1}$$

The specific rotation of (S)-carvone is (+)61°, measured 'neat' (pure liquid sample, no solvent). The optical rotation of a neat sample of a mixture of R and S carvone is measured at (-)23°. Which enantiomer is in excess, and what is its ee? What are the percentages of (R)- and (S)-carvone in the sample?

The observed rotation of the mixture is levorotary (negative, counter-clockwise), and the specific rotation of the pure S enantiomer is given as dextrorotary (positive, clockwise), meaning that the pure R enantiomer must be levorotary, and the mixture must contain more of the R enantiomer than of the S enantiomer.

Rotation (R/S Mix) = [Fraction(S) × Rotation (S)] + [Fraction(R) × Rotation (R)]

Let Fraction (S) = x, therefore Fraction (R) = 1 – x.

Rotation (R/S Mix) = x[Rotation (S)] + (1 – x)[Rotation (R)].

–23 = x(+61) + (1 – x)(–61)

(Video) 5.3 Optical Activity and Racemic Mixtures

Solve for x: x = 0.3114 and (1 – x) = 0.6885

Therefore the percentages of (R)- and (S)-carvone in the sample are 68.9% and 31.1%, respectively.

ee = [(% more abundant enantiomer – 50) × 100]/50. = [68.9 – 50) × 100]/50 = 37.8%.

Chiral molecules are often labeled according to the sign of their specific rotation, as in (S)-(+)-carvone and (R)-(-)-carvone, or (±)-carvone for the racemic mixture. However, there is no relationship whatsoever between a molecule's R/S designation and the sign of its specific rotation. Without performing a polarimetry experiment or looking in the literature, we would have no idea that (-)-carvone has the R configuration and (+)-carvone has the S configuration

Chiral molecules are often labeled according to the sign of their specific rotation, as in (S)-(+)-carvone and (R)-(-)-carvone, or (±)-carvone for the racemic mixture. However, there is no relationship whatsoever between a molecule's R/S designation and the sign of its specific rotation. Without performing a polarimetry experiment or looking in the literature, we would have no idea that (-)-carvone has the R configuration and (+)-carvone has the S configuration.

## Separation of Chiral Compounds

As noted earlier, chiral compounds synthesized from achiral starting materials and reagents are generally racemic (i.e. a 50:50 mixture of enantiomers). Separation of racemates into their component enantiomers is a process called resolution. Since enantiomers have identical physical properties, such as solubility and melting point, resolution is extremely difficult. Diastereomers, on the other hand, have different physical properties, and this fact is used to achieve resolution of racemates. Reaction of a racemate with an enantiomerically pure chiral reagent gives a mixture of diastereomers, which can be separated. For example, if a racemic mixture of a chiral alcohol is reacted with a enantiomerically pure carboxylic acid, the result is a mixture of diastereomers: in this case, because the pure (R) entantiomer of the acid was used, the product is a mixture of (R-R) and (R-S) diastereomeric esters, which can, in theory, be separated by their different physical properties. Subsequent hydrolysis of each separated ester will yield the 'resolved' (enantiomerically pure) alcohols. The used of this technique is known as chiral resolution.

##### Exercise $$\PageIndex{2}$$

A 3.20 g sample of morphine ([α]D = -132) was dissolved in 10.0 mL of acetic acid ([α]D = 0). If it is put into a sample tube with a path length of 2.00 cm, what would be its observed rotation (α)?

The specific rotation, [α]D = (observed rotation, α (degrees))/ [(pathlength, l (dm)) x (concentration, c (g/cm3))] = α/(l x c)

Solving for α, α = [α]D x l x c

([α]D = -132) x (l = 2.00 cm = 0.200 dm) x (c = 3.20 g / 10.0 cm3 = 0.320 g/cm3)

α = -132 x 0.200 dm x 0.320 g/cm3 = -8.45 o

##### Exercise $$\PageIndex{3}$$

Is the morphine in the previous excercise dextrorotatory or levorotatory?

Since morphine has a (-) rotation, it indicates that it rotates light to the left (counterclockwise) and morphine is levorotatory.
##### Exercise $$\PageIndex{4}$$

Label the following compounds as dextrorotatory or levorotatory.

a) sucrose ([α]D = + 66.7)

(Video) Optical Activity - Specific Rotation & Enantiomeric Excess - Stereochemistry Youtube

b) cholesterol ([α]D = - 31.5)

c) cocaine ([α]D = - 16)

d) chloroform ([α]D = 0)

a) sucrose ([α]D = + 66.7) dextrorotatory

b) cholesterol ([α]D = - 31.5) levorotatory

c) cocaine ([α]D = - 16) levorotatory

d) chloroform ([α]D = 0) neither, not optically active

##### Exercise $$\PageIndex{5a}$$

The specific rotation of (S)-carvone is (+) 61o when measured neat (pure liquid sample with no solvent). The optical rotation of a neat sample of a mixture of R and S carvone is measured at (-) 23 o.

a) Which enantiomer is in excess?

Since the pure S enantiomer ((+) 61o) is dextrorotatory (positive, clockwise), the R enantiomer must be levorotatory. The observed rotation of the mixture is levorotatory since its negative (counterclockwise). This means the mixture must contain more of the R enantiomer than the S enantiomer.

##### Exercise $$\PageIndex{5b}$$

b) What are the percentages of (S)- and (R)- carvone in the sample mixture?

Optical rotation (α) of the (R/S mixture) = [fraction (S) x [α]D (S)] + [fraction (R) x [α]D (R)]

To determine the fraction of S and R, we make y = fraction (S) and 1 – y = fraction (R)

-23o = y x (61o) + (1 – y) x (-61o) solving for y: y = 0.3114 and (1-y) = 0.6885

Therefore the percentage of (S)-carvone is 31.1 % and (R)-carvone is 68.9 %

##### Exercise $$\PageIndex{5c}$$

c) What is the ee (enantiomeric excess)?

ee = [(% more abundant isomer – 50) x 100]/50 = [(68.9 – 50) x100]/50 = 37.8 % ee

(Video) Chapter 5-3 Optical Activity
##### Exercise $$\PageIndex{6a}$$

Determine the ee’s of the following from the percentages

a) 95 % (R)- tartaric acid and 5.0 % (S)- tartaric acid

[(95 – 50) x 100] / 50 = 90 % ee (R)-tartaric acid

##### Exercise $$\PageIndex{6b}$$

b) 75 % (S)- limonene and 25 % (R)- limonene

[(75 – 50) x 100] / 50 = 50 % ee (S)- limonene

##### Exercise $$\PageIndex{6c}$$

c) 85 % (R) cysteine

(85 – 50) x 100] / 50 = 70 % ee (R)-cysteine

##### Exercise $$\PageIndex{6d}$$

d) 50 % (S) alanine

(50 – 50) x 100] / 50 = 0 % ee, racemic mixture

## FAQs

### How do you measure optical activity? ›

Measuring Optical Activity
1. [α] is the specific rotation in degrees cm3 dm-1 g-1.
2. λ is the wavelength in nanometers,
3. α is the measured angle of rotation of a substance,
4. T is the temperature in degrees,
5. l is the path length in decimeters,
6. c is the concentration in g/ml, and.
12 Sept 2020

What does optical activity tell us? ›

Optical activity is the ability of a chiral molecule to rotate the plane of plane-polairsed light, measured using a polarimeter. A simple polarimeter consists of a light source, polarising lens, sample tube and analysing lens.

How does concentration affect optical activity? ›

As concentration increases, the number of molecules possessing chiral properties also increases, resulting in greater optical rotation.

What is optical activity with example? ›

Substances that have the ability to rotate the plane of the polarized light passing through them are called optically active substances. Quartz and cinnabar are examples of optically active crystals while aqueous solutions of sugar, tartaric acid are optically active solutions.

How do you tell if it is optically active? ›

The Difference Between Enantiomers on the Macroscopic Scale

Because they interact with light, substances that can rotate plane-polarized light are said to be optically active. Those that rotate the plane clockwise (to the right) are said to be dextrorotatory (from the Latin dexter, "right").

What causes optical activity? ›

The cause of optical activity for a molecule is when the molecule is chiral. Optical activity is defined as the property shown by the compounds in which the plane of polarization is rotated for a plane-polarized light.

How is optical purity calculated? ›

To calculate the optical purity, divide the specific rotation of the sample by the specific rotation of the pure enantiomer, then multiply by 100.

Is water optically active? ›

Water has plane of symmetry. So it is achiral. It is achiral so it does not have optical chirality. However, one can observe optical polarization rotation in water using chirality induced by magnetic field (magnetic field direction being along the propagation of light).

Is Sugar optically active? ›

Sugar solutions are optically active, in other words they rotate the plane of polarisation of any linearly polarised light that is passed through them. The direction of rotation depends on the molecular properties of the sugar.

On what factors the optical activity of a medium depends? ›

The optical rotation exhibited by a chiral medium depends on the optical pathlength, the wavelength of the light used, the temperature of the system and the concentration of dissymmetric analyte molecules.

### How do you read a polarimeter scale? ›

The outer scale is the whole number for observed rotation reading and the inner scale is the decimal point for the observed rotation reading. To make the reading, note where the zero on the inner scale meets up with the numbers on the outer scale.

How do you calculate concentration from optical rotation? ›

Specific Rotation and Observed Rotation Calculations in Optical ...

What are the two types of optical activity? ›

Two types of optical activity can be discerned: birefringence (also called double refraction) and dichroism.

Are chiral optically inactive? ›

As stated, chiral molecules are optically active, which implies that when a beam of plane-polarized light passes through a chiral molecule, it interacts with the molecule in such a way that the angle of the plane of oscillation rotates.

What is optical activity PPT? ›

 Optical Activity Compounds “that rotate the plane of polarized light to the right (clockwise) are called dextrorotatory.”  d(+) IUPAC convention  “Compounds that rotate the plane of polarized light to the left (counterclockwise) are called levorotatory.”

What means optically active? ›

Definition of optically active

: capable of rotating the plane of vibration of polarized light to the right or left —used of compounds, molecules, or atoms.

How do you know if compounds are optically active or inactive? ›

Complete step by step answer: The compounds which are capable of optical rotation are said to be optically active compounds. All the chiral compounds are optically active. The chiral compound contains an asymmetric center where the carbon is attached with four different atoms or groups.

Which compound will show optical activity? ›

In compounds, C and D, the interconversion of one isomer into another isomer (mirror image) is not possible. Also, different groups are attached to the central N atom in both of these compounds. So, compounds C and D are optically active.

What is not optically active? ›

Solution : Trans complex is symmetrical and is optically inactive.

Who discovered optical activity? ›

Optical rotation—rotation of the plane of polarization of light as it propagates—was first discovered by Jean-Baptiste Biot in 1815, and it had an almost immediate impact by providing a quantitative measure of the purity of sugar. 1. T.

### What are the types of optically active substances? ›

There are two types of optically active substances. Substances of the first type, for example, sugars, camphor, and tartaric acid, are optically active in any state of aggregation. Substances of the second type, for example, quartz and cinnabar, are active only in the crystal phase.

What is optical purity of 6gm D and 4gm? ›

Answer : b. Solution : Optical purity or enantiomeric excess =("Exess of one enantiomer")/("Total mixture")xx100 <br> Enantiomeric exess (e.e.) =(6g-4g)/(6+4)xx100=20%

What does a 0% enantiomeric excess mean? ›

In stereochemistry, enantiomeric excess (ee) is a measurement of purity used for chiral substances. It reflects the degree to which a sample contains one enantiomer in greater amounts than the other. A racemic mixture has an ee of 0%, while a single completely pure enantiomer has an ee of 100%.

How do you calculate percentage purity? ›

Percentage purity of a substance can be calculated by dividing the mass of the pure chemical by the total mass of the sample, and then multiplying this number by 100.

Is sugar chiral? ›

Key molecules in nature, such as carbohydrates, amino acids, and nucleic acids, harbor chiral centers. Natural amino acids have L-chirality, whereas sugars have D-chirality, and living organisms typically use only one form of chiral molecules (Blackmond, 2010).

Why sodium lamp is used in polarimeter? ›

A polarimeter is defined as a scientific instrument that is used for measuring the angle of rotation caused by the passing of polarized light through an optically active substance. For this sodium light is used because it produces monochromatic light and the energy output is high.

Why is polarimeter used? ›

Polarimeters are used in a wide range of applications, from the determination of the purity and concentration of ingredients in pharmaceuticals to the maturity testing of agri cultural products to the measurement of the sugar con tent in beverages and candies.

Why is sucrose optically active? ›

The sucrose crystal exhibits a small natural optical activity in the visible range (400–800 nm) due to the spiral alignment of the sucrose molecule in the crystal structure.

Is lactic acid optically active? ›

Lactic acid is a chiral molecule because it has a chiral carbon atom or asymmetric carbon atom and is therefore optically active.

Why chiral compounds are optically active? ›

Because chiral molecules are able to rotate the plane of polarization differently by interacting with the electric field differently, they are said to be optically active. In general molecules that rotate light in differen directions are called optical isomers.

### Are all enantiomers optically active? ›

Enantiomers have identical chemical and physical properties and are indistinguishable from each other except for the direction of rotation of the plane of polarized light. They are described as optically active.

How is optical activity measured by polarimeter? ›

Measuring principle

A polarimeter is an instrument which measures the angle of rotation by passing polarized light through an optically active (chiral) substance. To measure optical rotation, a Light Emitting Diode (LED) produces a beam of ordinary light.

What is the least count of polarimeter? ›

It resembles with the 20 divisions of the circular scale (in degree). Therefore, the least count of the Vernier scale is 0.05o.

How do you calibrate a polarimeter? ›

5.2. 20 Rinse the tube with 10% solution and fill the solution in Polarimeter tube. 5.2.
...
5.2 Calibration
1. Switch 'On' the mains. ...
2. Wait till sodium lamp glows with the full intensity of yellow light. ...
3. Rinse the Polarimeter tube with distilled water. ...
4. Adjust the vernier scale and main dial scale to zero.

How do you determine concentration? ›

The standard formula is C = m/V, where C is the concentration, m is the mass of the solute dissolved, and V is the total volume of the solution. If you have a small concentration, find the answer in parts per million (ppm) to make it easier to follow.

What is specific rotation formula? ›

The specific rotation equation is expressed as follows; Specific rotation=[α]Tλ=observed rotation(degrees)length (dm) * Concentration (g/mL) Specific rotation = [ α ] λ T = observed rotation(degrees) length (dm) * Concentration (g/mL)

What is the ratio of enantiomers? ›

The '40% racemic' fraction consists of 20% of each enantiomer, so the ratio of the two enantiomers is major (60+20)%, minor 20%, i.e. 80:20.

Is Levorotatory R or S? ›

For example, the levorotatory (–) form of tartaric acid (S, S) is also sometimes described as D-tartaric acid for reasons we won't go in to here, and conversely, the dextrorotary form (R, R) is described as L-tartaric acid.

How do you know if R or S? ›

Draw an arrow starting from priority one and going to priority two and then to priority 3: If the arrow goes clockwise, like in this case, the absolute configuration is R. As opposed to this, if the arrow goes counterclockwise then the absolute configuration is S.

Why do enantiomers rotate light? ›

It means that when plane polarised light interacts with chiral centres, one of the two helixes slows down more than the other, and therefore goes out of synchronisation with the other one. Resolving the vectors demonstrates that the light rotates either left or right after passing through the chiral centre..

### Are all enantiomers chiral? ›

Are all enantiomers chiral? Chiral describes an atom that has four separate groups attached to it, while enantiomers describe the two stereoisomer relations. Enantiomers also have chiral centers in the molecules, but not all molecular stereoisomers are mutually enantiomers.

Which molecule is chiral? ›

A chiral molecule or ion exists in two stereoisomers that are mirror images of each other, called enantiomers; they are often distinguished as either "right-handed" or "left-handed" by their absolute configuration or some other criterion.

Which compound is not optically active? ›

Solution. Explanation: 3-chloropentane compound is not optically active.

What is the unit of specific rotation? ›

Specific rotation of a compound is a characteristic property of the compound as long as the temperature, the wave length of the light, and, if a solution is used for the experiment, the solvent are specified. The units of specific rotation are degreesmLg-1dm-1.

What is specific angle of rotation? ›

noun. : the angle of rotation in degrees of the plane of polarization of a ray of monochromatic light that passes through a tube 1 decimeter long containing the substance in solution at a concentration of 1 gram per millimeter in a polarimeter.

What is plane Polarised light? ›

Plane polarized light consists of waves in which the direction of vibration is the same for all waves. In circular polarization the electric vector rotates about the direction of propagation as the wave progresses.

What does A polarimeter measure? ›

A polarimeter measures the direction and extent of the polarisation plane rotation. Depending on the type of instrument, the analyser is rotated manually or automatically until the maximum intensity of the light falls on the detector.

How do you know if R or S? ›

Draw an arrow starting from priority one and going to priority two and then to priority 3: If the arrow goes clockwise, like in this case, the absolute configuration is R. As opposed to this, if the arrow goes counterclockwise then the absolute configuration is S.

What is optical activity in biochemistry? ›

Optical activity is the ability of a chiral molecule to rotate the plane of plane-polairsed light, measured using a polarimeter. A simple polarimeter consists of a light source, polarising lens, sample tube and analysing lens.

Which molecule will show optical activity? ›

In compounds, C and D, the interconversion of one isomer into another isomer (mirror image) is not possible. Also, different groups are attached to the central N atom in both of these compounds. So, compounds C and D are optically active.

### How do you read polarimeter results? ›

The outer scale is the whole number for observed rotation reading and the inner scale is the decimal point for the observed rotation reading. To make the reading, note where the zero on the inner scale meets up with the numbers on the outer scale.

Is water optically active? ›

Water has plane of symmetry. So it is achiral. It is achiral so it does not have optical chirality. However, one can observe optical polarization rotation in water using chirality induced by magnetic field (magnetic field direction being along the propagation of light).

Which light is used in polarimeter? ›

A polarimeter is defined as a scientific instrument that is used for measuring the angle of rotation caused by the passing of polarized light through an optically active substance. For this sodium light is used because it produces monochromatic light and the energy output is high.

Why is ch2 higher priority than ch3? ›

For example, the ethenyl group (CH2=CH) has higher priority than the ethyl group (CH3CH2). The ethenyl carbon priority is "two" bonds to carbon atoms and one bond to a hydrogen atom compared with the ethyl carbon that has only one bond to a carbon atom and two bonds to two hydrogen atoms.

Is 2R 3S Dibromobutane a meso compound? ›

Since (2R,3S) and (2S,3R)-2,3-dibromobutane (Figures [graphic 4.27] and [graphic 4.28]) are identical to each other (superimposable on each other), they are a single stereoisomer that we call a meso form or meso isomer.

Is R clockwise or counter? ›

If the lowest priority group is in front of this curved arrow, then the assignment is reversed: clockwise is S and counterclockwise is R. (Basically, you are looking at the steering wheel from the perspective of the engine compartment!)

Is sugar optically active? ›

Sugar solutions are optically active, in other words they rotate the plane of polarisation of any linearly polarised light that is passed through them. The direction of rotation depends on the molecular properties of the sugar.

How is optical purity calculated? ›

To calculate the optical purity, divide the specific rotation of the sample by the specific rotation of the pure enantiomer, then multiply by 100.

Why chiral molecules are optically active? ›

Because chiral molecules are able to rotate the plane of polarization differently by interacting with the electric field differently, they are said to be optically active. In general molecules that rotate light in differen directions are called optical isomers.

Which of the following compound is optically active Mcq? ›

2-chlorobutane contains one chiral carbon. So, it is optically active.

### Who does not show optical activity? ›

Meso compounds don't exhibit optical activity because of the presence of a plane of symmetry because of which optical activity cancels out.

Is CH3CHO optically active? ›

In the process of Ozonolysis, one molecule of the given compound results in the formation of two products such as CH3CHO and OHCHCH(CH3)CHO, having two molecules each. None of these two is optically active.

## Videos

1. Polarised light and optical activity
(Chemistry Channel)
2. Optical Rotation Demonstration Polaroid and Glucose
(Farnborough Chemistry)
3. Optical Activity and Optically Active Molecules
(Andrey K)
4. Optical activity calculations | Stereochemistry | Organic chemistry | Khan Academy
5. Optical activity | Plane-Polarized Light 🌟
(Fun Man Fung, Ph.D.)
6. Lecture 5.3 Enantiomers and Optical Rotation
(Lemieux Chem)
Top Articles
Latest Posts
Article information

Author: Greg Kuvalis

Last Updated: 03/04/2023

Views: 6341

Rating: 4.4 / 5 (75 voted)

Author information

Name: Greg Kuvalis

Birthday: 1996-12-20

Address: 53157 Trantow Inlet, Townemouth, FL 92564-0267

Phone: +68218650356656

Job: IT Representative

Hobby: Knitting, Amateur radio, Skiing, Running, Mountain biking, Slacklining, Electronics

Introduction: My name is Greg Kuvalis, I am a witty, spotless, beautiful, charming, delightful, thankful, beautiful person who loves writing and wants to share my knowledge and understanding with you.