Slide 2: Haloalkanes and Haloarenes

• Haloalkanes are compounds that contain a halogen atom (fluorine, chlorine, bromine, or iodine) bonded to a carbon atom
• Haloarenes are compounds that contain a halogen atom bonded to an aromatic ring
• Both haloalkanes and haloarenes can exhibit optical activity when they have an asymmetric carbon or an asymmetric carbon within the ring, respectively

Slide 3: Asymmetric Carbon in Haloalkanes

• An asymmetric carbon is a carbon atom that is bonded to four different groups
• In haloalkanes, an asymmetric carbon leads to optical activity
• Optical activity arises due to the spatial arrangement of the groups around the asymmetric carbon

Slide 4: Chirality in Haloalkanes

• Chirality refers to the property of having a nonsuperimposable mirror image
• Haloalkanes with an asymmetric carbon are chiral compounds
• Chiral compounds exist as a pair of enantiomers, which are mirror images of each other

Slide 5: Enantiomers

• Enantiomers have the same physical and chemical properties except for their interactions with plane-polarized light
• Enantiomers rotate plane-polarized light either to the left (Levorotatory - symbol “(-)”) or right (Dextrorotatory - symbol “(+)”)
• The amount of rotation is given by the specific rotation (α)

Slide 6: Specific Rotation

• Specific rotation (α) is a measure of the amount and direction of optical rotation
• It is defined as the observed rotation (observed with a polarimeter) divided by the concentration of the compound and the path length of the solution
• Specific rotation is expressed in units of degrees per unit concentration and path length (°/(g·cm))

Slide 7: Calculation of Specific Rotation

• To calculate specific rotation, we use the formula: α = α_observed / (c * l)
• α_observed is the observed rotation in degrees
• c is the concentration of the compound in g/mL
• l is the path length of the polarimeter tube in cm
• The sign of α indicates whether the compound is levorotatory or dextrorotatory

Slide 8: Optical Activity in Haloarenes

• Haloarenes can also show optical activity if they have an asymmetric carbon within the ring
• In haloarenes, optical activity arises due to the spatial arrangement of the groups around the asymmetric carbon in the aromatic ring

Slide 9: Optically Active Haloarenes

• Just like in haloalkanes, an asymmetric carbon in haloarenes leads to optical activity
• The optical rotation of haloarenes is also measured using a polarimeter and expressed in terms of specific rotation
• The specific rotation of optically active haloarenes can be calculated using the same formula as for haloalkanes

Slide 10: Examples of Optically Active Compounds

• Let’s explore some examples of optically active haloalkanes and haloarenes:
  • (S)-2-Chlorobutane: An optically active haloalkane, with the chlorine atom bonded to an asymmetric carbon
  • (R)-1-Bromo-3-chlorocyclohexane: An optically active haloarene, with the bromine and chlorine atoms bonded to an asymmetric carbon in the aromatic ring

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21. Optical Activity in Haloalkanes:

• Haloalkanes with an asymmetric carbon exhibit optical activity
• The presence of different substituents around the asymmetric carbon results in nonsuperimposable mirror images
• These mirror images are called enantiomers
• Enantiomers have identical physical and chemical properties except for their interaction with plane-polarized light
• The specific rotation of enantiomers can be determined experimentally

22. Calculation of Specific Rotation in Haloalkanes:

• Specific rotation (α) is calculated using the formula: α = α_observed / (c * l)
• α_observed is the observed rotation in degrees
• c is the concentration of the compound in g/mL
• l is the path length of the polarimeter tube in cm
• The sign of α indicates the direction of rotation (levorotatory or dextrorotatory)

23. Optical Activity in Haloarenes:

• Haloarenes can also exhibit optical activity if they possess an asymmetric carbon within the aromatic ring
• The spatial arrangement of substituents around the asymmetric carbon determines the optical activity
• Just like in haloalkanes, haloarenes exist as enantiomeric pairs

24. Racemic Mixture:

• A racemic mixture is a 50:50 mixture of two enantiomers
• It does not exhibit optical activity because the rotations of the two enantiomers cancel out
• Racemic mixtures are indicated by a (+/-) prefix in their names or by a racemic symbol (dotted line) in their structural formulas

25. Resolving Agents:

• Resolving agents can be used to separate enantiomers from a racemic mixture
• They selectively react with one enantiomer, converting it into a diastereomer or a salt that can be separated from the other enantiomer
• Common resolving agents include tartaric acid, cinchona alkaloids, and chiral stationary phase columns in chromatography

26. Chiral Drugs:

• Optical activity is relevant in pharmaceuticals because some enantiomers exhibit different biological activities
• One enantiomer may have the desired therapeutic effect, while the other may be inactive or even have adverse effects
• Chiral drugs are typically formulated as single enantiomers to ensure maximum efficacy and safety

27. Examples of Optically Active Compounds:

• (S)-2-Chlorobutane: An optically active haloalkane with an asymmetric carbon
• (R)-1-Bromo-3-chlorocyclohexane: An optically active haloarene with an asymmetric carbon in the aromatic ring
• Both compounds exist as pairs of enantiomers and show optical rotation

28. Importance of Optical Activity in Chemical Industries:

• Optical activity is relevant in the production of pharmaceuticals, flavors, fragrances, and agrochemicals
• Enantiomerically pure compounds are required to ensure desired therapeutic effects and minimize side effects
• Optical activity also plays a role in the synthesis of chiral ligands catalysts for asymmetric synthesis

29. Stereochemistry and Molecular Recognition:

• Optical activity is linked to stereochemistry, which focuses on the three-dimensional arrangement of atoms in molecules
• Enantiomers can have different interactions with other chiral molecules or biomolecules due to their unique stereochemical properties
• This can affect molecular recognition, receptor binding, and biological activity

30. Conclusion:

• Haloalkanes and haloarenes with an asymmetric carbon can exhibit optical activity
• Enantiomers are mirror images but not superimposable
• Specific rotation quantifies optical activity, with α indicating the direction of rotation
• Optical activity is relevant in pharmaceuticals, chemical industries, and molecular recognition processes
• Resolving agents and chiral drug formulations are used to isolate and utilize specific enantiomers for desired effects.