Haloakanes and Haloarenes
- Haloakanes and Haloarenes are organic compounds that contain halogen atoms.
- The halogen atoms in these compounds can be chlorine (Cl), bromine (Br), iodine (I), or fluorine (F).
- Haloakanes have a halogen atom bonded to an alkyl group, while haloarenes have a halogen atom bonded to an aromatic ring.
- Both haloakanes and haloarenes are widely used in various industries and have important applications in organic synthesis.
- The presence of halogen atoms in these compounds affects their physical and chemical properties, making them distinct from other organic compounds.
Plane Polarized Light and Optical Activity
- Plane polarized light is a type of light in which the vibrations of the electric field are limited to a single plane.
- When plane polarized light passes through certain substances, the plane of polarization gets rotated. This is known as optical activity.
- Optical activity is observed in compounds that have a chiral center, which means they have a stereocenter and are not superimposable on their mirror image.
- Compounds that exhibit optical activity can exist in two forms known as enantiomers, which are mirror images of each other.
- The ability of a compound to rotate the plane of polarized light is dependent on factors such as the nature of the compound, concentration, and path length.
Types of Optical Activity
- Optical activity can be either dextro-rotatory (d) or laevo-rotatory (l) depending on the direction of rotation.
- Dextro (d)-rotatory compounds rotate the plane of polarized light in a clockwise direction (to the right).
- Laevo (l)-rotatory compounds rotate the plane of polarized light in an anti-clockwise direction (to the left).
- The direction of rotation is determined by comparing the observed rotation with a standard substance.
- Optical activity can be measured using a polarimeter which allows us to quantify the angle of rotation.
- The magnitude of the rotation is represented by the specific rotation, denoted by [α]. The formula for specific rotation is [α] = α/lc, where α is the observed rotation, l is the path length, and c is the concentration.
Factors Affecting Optical Activity
- The presence of a chiral center is the primary factor for a compound’s optical activity.
- An increase in the number of chiral centers in a compound results in greater optical activity.
- The nature of the substituents attached to the chiral center can also influence the degree of optical activity.
- Temperature and solvent choice can affect the magnitude of optical rotation.
- Concentration also plays a role; for a pure enantiomer, the concentration has no effect on optical activity.
RacemicMixture and Polarimetry
- A mixture that contains equal amounts of both enantiomers is called a racemic mixture or a racemate.
- A racemate shows no optical activity as the rotations of its two enantiomers cancel each other out.
- Racemic mixtures can be detected by measuring the rotation of plane polarized light using a polarimeter.
- Polarimetry is a common technique used to measure the optical activity of a compound.
- By comparing the rotation of an unknown compound with the rotation of known standards, the enantiomeric purity and identity of the compound can be determined.
Specific Rotation and Enantiomeric Excess
- Specific rotation ([α]) is the angle of rotation observed using a polarimeter for a given compound.
- The specific rotation varies with the wavelength of light used and the temperature at which the measurement is taken.
- Enantiomeric excess (ee) is a measure of how much one enantiomer is present in excess of the other in a sample.
- It is expressed as a percentage and can be calculated using the formula: ee = [(αobserved) / (αmax)] * 100.
- A sample with an enantiomeric excess of 100% contains only one enantiomer, while a racemic mixture has an enantiomeric excess of 0%.
Applications of Optical Activity
- Optical activity has numerous applications in various fields, including pharmaceuticals, food industry, and chemical synthesis.
- In the pharmaceutical industry, optical activity is utilized in the development and manufacturing of chiral drugs.
- Optical activity is crucial in determining the purity and identity of drugs, as enantiomers can exhibit different biological activities.
- In the food industry, optical activity is used to analyze and control the quality of food products, especially those containing chiral molecules.
- Chiral compounds exhibit different tastes, odors, and textures, which can greatly impact the sensory experience of food.
Examples of Optically Active Compounds
- One example of an optically active compound is (+)-limonene, which is found in citrus fruits and has a characteristic orange scent.
- Lactic acid, present in sour milk, yogurt, and pickles, is another example of an optically active compound.
- Many drugs contain chiral centers and exhibit optical activity. For example, ibuprofen and naproxen are chiral drugs used as pain relievers.
- Natural occurring sugars such as glucose and fructose are also optically active compounds.
- Optical activity is a common property observed in organic compounds, and its applications are diverse and significant.
Properties of Haloalkanes
- Haloalkanes have higher boiling points than their corresponding alkanes due to the presence of the polar C-X bond.
- They are insoluble in water but soluble in organic solvents.
- Haloalkanes can undergo nucleophilic substitution reactions due to the presence of a polarized C-X bond.
- They are less reactive than alkenes and alkynes but more reactive than alkanes.
- The reactivity of haloalkanes increases with the size and polarizability of the halogen atom.
Nomenclature of Haloalkanes
- The halogen atom in haloalkanes is named as a substituent using the prefix fluoro-, chloro-, bromo-, or iodo-.
- The parent hydrocarbon chain is named according to the number of carbon atoms.
- The functional group priority is given to the halogen over any other functional group present.
- Numbering of the carbon atoms is done in such a way that the halogen atom gets the lowest possible number.
Physical properties of Haloarenes
- Haloarenes have higher boiling points than haloalkanes due to the presence of π-electron cloud in benzene ring.
- They are insoluble in water but soluble in organic solvents.
- Substituents attached to the benzene ring can affect the physical properties of haloarenes.
- The presence of halogen atoms in haloarenes enhances their reactivity compared to the benzene ring.
- The reactivity of haloarenes depends on the nature and position of the halogen atom.
Nomenclature of Haloarenes
- The halogen atom in haloarenes is named as a substituent using the prefix fluoro-, chloro-, bromo-, or iodo-.
- The parent aromatic hydrocarbon is named according to the number of carbon atoms in the ring.
- The functional group priority is given to the halogen over any other substituents attached to the benzene ring.
- Numbering of the carbon atoms is done in such a way that the halogen atom gets the lowest possible number.
Preparation of Haloalkanes
- Haloalkanes can be prepared from alkanes via a free radical substitution reaction.
- Example: Chlorination of Methane (CH4 + Cl2 → CH3Cl + HCl)
- Haloalkanes can be prepared from alcohols via an acidic substitution reaction.
- Example: Conversion of Ethanol to Ethyl Chloride (CH3CH2OH + HCl → CH3CH2Cl + H2O)
- Haloalkanes can be prepared from alkyl halides via a nucleophilic substitution reaction.
- Example: Reaction of Alkyl Halide with a Strong Nucleophile (R-X + Nuc- → R-Nuc + X-)
Preparation of Haloarenes
- Haloarenes can be prepared from benzene via an electrophilic substitution reaction.
- Example: Chlorination of Benzene (C6H6 + Cl2 → C6H5Cl + HCl)
- Haloarenes can be prepared from phenols via an electrophilic aromatic substitution reaction.
- Example: Conversion of Phenol to Chlorobenzene (C6H5OH + HCl → C6H5Cl + H2O)
- Haloarenes can be prepared from aniline via an electrophilic aromatic substitution reaction.
- Example: Conversion of Aniline to Chlorobenzene (C6H5NH2 + HCl → C6H5Cl + NH4Cl)
Reactions of Haloalkanes
- Nucleophilic Substitution Reactions:
- Haloalkanes can undergo substitution reactions in the presence of a nucleophile.
- Examples: SN1 and SN2 reactions.
- Elimination Reactions:
- Haloalkanes can undergo elimination reactions to form alkenes or alkynes.
- Examples: E1 and E2 reactions.
- Reduction Reactions:
- Haloalkanes can be reduced to alkanes using reducing agents.
- Example: Reduction of Haloalkanes using Na/ether.
- Reaction with Metals:
- Some haloalkanes react with metals to form metal alkyl compounds.
- Example: Reaction of Grignard reagents with haloalkanes.
Reactions of Haloarenes
- Nucleophilic Aromatic Substitution (SNAr) Reactions:
- Haloarenes can undergo substitution reactions in the presence of a nucleophile.
- Examples: Addition-Elimination (A-E) and Elimination-Addition (E-A) mechanisms.
- Electrophilic Aromatic Substitution (SEAr) Reactions:
- Haloarenes can undergo substitution reactions with electrophiles.
- Examples: Nitration, Halogenation, Friedel-Crafts reactions.
- Reduction Reactions:
- Haloarenes can be reduced to corresponding alkyl benzene compounds using reducing agents.
- Example: Reduction of Haloarenes using H2/Raney Nickel.
- Metal-Halogen Exchange:
- Haloarenes can undergo reaction with metals to form aryl-metal compounds.
- Example: Reaction of Haloarenes with Grignard reagents.
Environmental Impact of Haloalkanes and Haloarenes
- Some haloalkanes and haloarenes are classified as Persistent Organic Pollutants (POPs) and can enter the environment through various human activities.
- POPs can have detrimental effects on the environment and human health due to their resistance to degradation and accumulation in living organisms.
- Examples of POPs include polychlorinated biphenyls (PCBs), dioxins, and certain organochlorine pesticides.
- Strict regulations have been put in place to control the production, use, and disposal of haloalkanes and haloarenes to minimize their impact on the environment.
Industrial Applications of Haloalkanes and Haloarenes
- Haloalkanes and haloarenes have broad industrial applications in various fields.
- They are used as solvents for cleaning, degreasing, and extraction purposes.
- Some haloalkanes and haloarenes are used as refrigerants due to their low boiling points.
- They are employed in the pharmaceutical industry as intermediates in the synthesis of drugs.
- Haloalkanes and haloarenes are used as monomers in the production of polymers and plastics.
- They find application in the production of agrochemicals such as insecticides and herbicides.
Slide 21: Haloakanes and Haloarenes - Plane Polarized Light and Optical Activity
- Plane polarized light is a type of light in which the vibrations of the electric field are limited to a single plane.
- When plane polarized light passes through certain substances, the plane of polarization gets rotated. This is known as optical activity.
- Optical activity is observed in compounds that have a chiral center, which means they have a stereocenter and are not superimposable on their mirror image.
- Compounds that exhibit optical activity can exist in two forms known as enantiomers, which are mirror images of each other.
- The ability of a compound to rotate the plane of polarized light is dependent on factors such as the nature of the compound, concentration, and path length.
Slide 22: Types of Optical Activity
- Optical activity can be either dextro-rotatory (d) or laevo-rotatory (l) depending on the direction of rotation.
- Dextro (d)-rotatory compounds rotate the plane of polarized light in a clockwise direction (to the right).
- Laevo (l)-rotatory compounds rotate the plane of polarized light in an anti-clockwise direction (to the left).
- The direction of rotation is determined by comparing the observed rotation with a standard substance.
- Optical activity can be measured using a polarimeter which allows us to quantify the angle of rotation.
Slide 23: Factors Affecting Optical Activity
- The presence of a chiral center is the primary factor for a compound’s optical activity.
- An increase in the number of chiral centers in a compound results in greater optical activity.
- The nature of the substituents attached to the chiral center can also influence the degree of optical activity.
- Temperature and solvent choice can affect the magnitude of optical rotation.
- Concentration also plays a role; for a pure enantiomer, the concentration has no effect on optical activity.
Slide 24: Racemic Mixture and Polarimetry
- A mixture that contains equal amounts of both enantiomers is called a racemic mixture or a racemate.
- A racemate shows no optical activity as the rotations of its two enantiomers cancel each other out.
- Racemic mixtures can be detected by measuring the rotation of plane polarized light using a polarimeter.
- Polarimetry is a common technique used to measure the optical activity of a compound.
- By comparing the rotation of an unknown compound with the rotation of known standards, the enantiomeric purity and identity of the compound can be determined.
Slide 25: Specific Rotation and Enantiomeric Excess
- Specific rotation ([α]) is the angle of rotation observed using a polarimeter for a given compound.
- The specific rotation varies with the wavelength of light used and the temperature at which the measurement is taken.
- Enantiomeric excess (ee) is a measure of how much one enantiomer is present in excess of the other in a sample.
- It is expressed as a percentage and can be calculated using the formula: ee = [(αobserved) / (αmax)] * 100.
- A sample with an enantiomeric excess of 100% contains only one enantiomer, while a racemic mixture has an enantiomeric excess of 0%.
Slide 26: Applications of Optical Activity
- Optical activity has numerous applications in various fields, including pharmaceuticals, food industry, and chemical synthesis.
- In the pharmaceutical industry, optical activity is utilized in the development and manufacturing of chiral drugs.
- Optical activity is crucial in determining the purity and identity of drugs, as enantiomers can exhibit different biological activities.
- In the food industry, optical activity is used to analyze and control the quality of food products, especially those containing chiral molecules.
- Chiral compounds exhibit different tastes, odors, and textures, which can greatly impact the sensory experience of food.
Slide 27: Examples of Optically Active Compounds
- One example of an optically active compound is (+)-limonene, which is found in citrus fruits and has a characteristic orange scent.
- Lactic acid, present in sour milk, yogurt, and pickles, is another example of an optically active compound.
- Many drugs contain chiral centers and exhibit optical activity. For example, ibuprofen and naproxen are chiral drugs used as pain relievers.
- Natural occurring sugars such as glucose and fructose are also optically active compounds.
- Optical activity is a common property observed in organic compounds, and its applications are diverse and significant.
Slide 28: Properties of Haloalkanes
- Haloalkanes have higher boiling points than their corresponding alkanes due to the presence of the polar C-X bond.
- They are insoluble in water but soluble in organic solvents.
- Haloalkanes can undergo nucleophilic substitution reactions due to the presence of a polarized C-X bond.
- They are less reactive than alkenes and alkynes but more reactive than alkanes.
- The reactivity of haloalkanes increases with the size and polarizability of the halogen atom.
Slide 29: Nomenclature of Haloalkanes
- The halogen atom in haloalkanes is named as a substituent using the prefix fluoro-, chloro-, bromo-, or iodo-.
- The parent hydrocarbon chain is named according to the number of carbon atoms.
- The functional group priority is given to the halogen over any other functional group present.
- Numbering of the carbon atoms is done in such a way that the halogen atom gets the lowest possible number.
Slide 30: Physical properties of Haloarenes
- Haloarenes have higher boiling points than haloalkanes due to the presence of π-electron cloud in benzene ring.
- They are insoluble in water but soluble in organic solvents.
- Substituents attached to the benzene ring can affect the physical properties of haloarenes.
- The presence of halogen atoms in haloarenes enhances their reactivity compared to the benzene ring.
- The reactivity of haloarenes depends on the nature and position of the halogen atom.
Haloakanes and Haloarenes Haloakanes and Haloarenes are organic compounds that contain halogen atoms. The halogen atoms in these compounds can be chlorine (Cl) , bromine (Br) , iodine (I) , or fluorine (F) . Haloakanes have a halogen atom bonded to an alkyl group, while haloarenes have a halogen atom bonded to an aromatic ring. Both haloakanes and haloarenes are widely used in various industries and have important applications in organic synthesis. The presence of halogen atoms in these compounds affects their physical and chemical properties, making them distinct from other organic compounds.