Functional Group Chemistry and Hydrocarbons

Functional Group Concepts

• Functional groups are defined by atom connectivity; different atoms (O, N, etc.) create distinct groups with characteristic properties.

• Groups within the same family react similarly; classification helps predict reactivity (e.g., alcohols).

• Alkene vs. alkane example: alkenes contain an sp^2-hybridized carbon and a C=C double bond, enabling addition reactions that change hybridization; alkanes lack double bonds and mainly undergo different, less reactive processes.

Hydrocarbon Families

• Alkane

  • sp^3-hybridized carbons; saturated (no C=C or C≡C); general formula R–H and R–R bonds; suffix -ane.

  • Example: propane.

• Alkene

  • sp^2-hybridized carbons; at least one C=C; unsaturated; suffix -ene.

  • Example concept: cyclopropane is a cycloalkane (see below).

• Cycloalkanes

  • Cyclic alkanes; prefix cyclo- with -ane; ring closures typically reduce hydrogen count by two per ring.

• Alkyne

  • Contains at least one C≡C triple bond; sp-hybridized; unsaturated; suffix -yne; hydrogen deficiency per multiple bond: 4 hydrogens.

• Aromatic compounds (benzene as classic example)

  • Planar, cyclic, alternating single/double bonds; delocalized π electrons; typically written with resonance structures; often described by a resonance hybrid.

  • Stability greater than expected due to delocalization; bond lengths are equivalent around the ring.

  • Huckel rule: pi electrons = 4n+2; benzene has 6 pi electrons (fits 4(1)+2=6).

Benzene and Resonance

• Benzene structure has p orbitals above and below the ring; electrons delocalize across the ring (delocalization).

• Resonance hybrids best describe benzene rather than a single alternating single/double pattern.

• Practical note: benzene bonds are of equal length due to delocalization.

Naming and Parent Names

• Alkanes: longest continuous carbon chain defines the parent name; add -ane.

  • 1 carbon: meth-; 2 carbons: eth-; 3: prop-; 4: but-; memorize up to 10 for quick recall.

• Cycloalkanes use the cyclo- prefix with -ane.

• Memorize common names; many charts list 1–10 for quick reference.

Alkyl Substituents and Arenes

• Alkyl groups: derived by removing one H from an alkane; named methyl, ethyl, propyl, isopropyl, etc.

  • Attachment can be at terminal or secondary carbons (isopropyl attaches through the middle carbon).

• Arenes: aromatic substituents can be named as arene groups; common forms include phenyl (Ph–) and benzyl (Bn–).

  • Phenyl vs. benzyl distinction matters for nomenclature and structure (Ph– versus –CH2–Ph).

• Representations: Ph–, C6H5–, or Bn– for benzyl groups.

Haloalkanes (Alkyl Halides)

• Halogen is attached to an alkyl group; suffixes may be haloalkane or alkyl halide.

• Primary, secondary, tertiary classifications refer to the carbon bearing the halogen:

  • Primary: halogen-bearing carbon attached to only one other carbon.

  • Secondary: halogen-bearing carbon attached to two other carbons.

  • Tertiary: halogen-bearing carbon attached to three other carbons.

• Quaternary carbon cannot form a halide (no hydrogens left to replace).

• Alkenyl halide: halogen attached to a double bond (alkenyl halide).

• Aryl halide: halogen attached to an aryl (e.g., phenyl) ring.

Alcohols and Phenols

• Alcohols: OH group attached to an sp³ carbon; can view as either alkyl derivative of water or alkane with OH substitution.

• Primary alcohol: OH on a carbon attached to one other carbon.

• Secondary alcohol: OH on a carbon attached to two other carbons.

• Tertiary alcohol: OH on a carbon attached to three other carbons.

• Examples: geraniol, benzyl alcohol, isopropyl alcohol, menthol.

• Phenols: OH attached directly to an aromatic ring; more acidic than typical alcohols due to resonance.

• Examples: estradiol, tetracyclines (aromatic phenolic groups).

Ethers

• Ethers: R-O-R' structure; two alkyl (or aryl) groups on oxygen.

• Examples: dimethyl ether (Me–O–Me), diethyl ether (Et–O–Et).

• THF (tetrahydrofuran) is a cyclic ether; ethylene oxide is a simple epoxide (three-membered ring ether).

• Fluorinated ethers: higher polarity due to C–F bonds; reduced volatility because of dipole-dipole interactions.

Amines

• Amines: ammonia with one or more hydrogens replaced by R groups; general form R3N, R2NH, RNH_2.

• Primary amine: nitrogen attached to one R group (e.g., RNH_2).

• Secondary amine: nitrogen attached to two R groups (e.g., R_2NH).

• Tertiary amine: nitrogen attached to three R groups (e.g., R_3N).

• Classification for amines is based on the number of R groups attached to nitrogen, not the number of hydrogens on nitrogen.

Functional Group Concepts (In-Depth)

• Definition and Classification: Functional groups are specific groupings of atoms within molecules that exhibit characteristic chemical reactions. The identity of these atoms (e.g., oxygen in alcohols, nitrogen in amines, halogens in haloalkanes) dictates the functional group and its properties. For instance, the presence of an OH group defines an alcohol, while a C=O defines a carbonyl, each with distinct reactivity patterns.

• Predicting Reactivity: Molecules with similar functional groups tend to undergo similar types of reactions, allowing for the prediction of chemical behavior. For example, all alcohols can typically undergo oxidation reactions, and compounds with C=C double bonds (alkenes) typically undergo addition reactions.

• Hybridization and Reactivity: The hybridization state of carbon atoms significantly impacts molecular geometry and reactivity. For instance:

  • Alkenes: Contain an sp^2-hybridized carbon atom participating in a carbon-carbon double bond (C=C). This double bond is a region of high electron density and acts as a nucleophile, readily undergoing addition reactions where the hybridization changes from sp^2 to sp^3. The presence of the \pi bond also allows for cis/trans isomerism.

  • Alkanes: Consist solely of sp^3-hybridized carbon atoms and single bonds (C-C and C-H). They are saturated, meaning they contain the maximum number of hydrogens, and are relatively unreactive, primarily undergoing substitution reactions (e.g., free radical halogenation) or combustion.

Hydrocarbon Families (In-Depth)

• Alkanes: Saturated hydrocarbons composed entirely of sp^3-hybridized carbon atoms and hydrogen atoms linked by single bonds. Their general formula is CnH{2n+2}. They are characterized by free rotation around their C-C single bonds, leading to various conformations (e.g., staggered, eclipsed for ethane).

  • Examples: Methane (CH4), Ethane (CH3CH3), Propane (CH3CH2CH3).

• Alkenes: Unsaturated hydrocarbons containing at least one carbon-carbon double bond (C=C). The carbons involved in the double bond are sp^2-hybridized and planar. Their general formula is CnH{2n} (for acyclic monoalkenes). The \pi bond is a source of reactivity, undergoing electrophilic addition.

  • Isomerism: Due to restricted rotation around the double bond, alkenes can exhibit cis-trans (geometric) isomerism if each carbon of the double bond is attached to two different groups.

• Cycloalkanes: Alkanes that form a closed ring structure. Their general formula is CnH{2n}, reflecting the loss of two hydrogens upon ring formation compared to an open-chain alkane.

  • Ring Strain: Small rings (cyclopropane, cyclobutane) exhibit significant angle strain due to deviation from the ideal 109.5^ ext{o} bond angles of sp^3 carbons, making them more reactive. Cyclohexane, in its chair conformation, is largely free of strain.

• Alkynes: Unsaturated hydrocarbons containing at least one carbon-carbon triple bond (C\equiv C). The carbons involved are sp-hybridized and linear. Their general formula is CnH{2n-2} (for acyclic monoalkynes). Terminal alkynes (where the triple bond is at the end of the chain, R-C\equiv C-H) are weakly acidic due to the sp hybridization of the terminal carbon, allowing for deprotonation by strong bases to form acetylide anions.

• Aromatic Compounds (Arenes): These are cyclic, planar molecules that exhibit special stability due to the delocalization of \pi electrons. Benzene (C6H6) is the quintessential example.

  • Aromaticity Criteria (Hückel's Rule): A compound is aromatic if it is cyclic, planar, fully conjugated (every atom in the ring has a p-orbital), and contains (4n+2) \pi electrons (where n is a non-negative integer). For benzene, n=1, so it has (4(1)+2)=6 \pi electrons.

  • Stability: The delocalization of \pi electrons imparts significant resonance stabilization, making aromatic compounds much more stable and less reactive towards addition reactions compared to simple alkenes. They primarily undergo electrophilic aromatic substitution reactions, retaining their aromaticity.

Benzene and Resonance (In-Depth)

• Atomic Orbitals: In benzene, each of the six carbon atoms is sp^2-hybridized, with the remaining unhybridized p-orbital on each carbon perpendicular to the plane of the ring. These six p-orbitals overlap laterally both above and below the ring, creating a continuous \pi -electron cloud.

• Resonance Hybrids: Benzene cannot be accurately represented by a single Lewis structure with alternating single and double bonds (Kekulé structures). Instead, it is best described as a resonance hybrid of two equivalent Kekulé structures. The actual structure is an average of these contributing forms.

• Bond Lengths: A key experimental observation supporting resonance in benzene is that all carbon-carbon bond lengths in the ring are identical (1.39 \mathring{A} or 0.139 \text{ nm}). This value is intermediate between a typical C-C single bond (1.54 \mathring{A}) and a typical C=C double bond (1.34 \mathring{A}), confirming the delocalized nature of the electrons.

Naming and Parent Names (In-Depth)

• IUPAC Nomenclature: Organic compounds are systematically named according to IUPAC (International Union of Pure and Applied Chemistry) rules.

  • Alkanes: The longest continuous carbon chain determines the parent name. Substituents are then numbered from the end of the chain that gives the lowest numbers to the substituents. Prefixes indicate the number of carbons:

    • 1 carbon: meth-

    • 2 carbons: eth-

    • 3 carbons: prop-

    • 4 carbons: but-

    • 5 carbons: pent-

    • …up to 10 carbons: dec- (e.g., undec- for 11, dodec- for 12).

  • Cycloalkanes: Named by adding the prefix 'cyclo-' to the alkane name corresponding to the number of carbons in the ring (e.g., cyclopropane, cyclohexane). If there are substituents, numbering starts from a substituent and proceeds around the ring to give the lowest possible numbers to other substituents.

• Common Names: Many compounds retain common or trivial names, which are important to memorize (e.g., isobutane for 2-methylpropane).

Alkyl Substituents and Arenes (In-Depth)

• Alkyl Groups: Formed by removing one hydrogen atom from an alkane. They are named by replacing the '-ane' suffix of the parent alkane with '-yl'.

  • Examples:

    • Methyl (-CH_3) from methane.

    • Ethyl (-CH2CH3) from ethane.

    • Propyl (-CH2CH2CH_3) from propane.

    • Isopropyl (CH3CH(CH3)-) from propane, attached at the middle carbon.

    • Butyl (-CH2CH2CH2CH3), sec-butyl (CH3CH(CH2CH3)-), tert-butyl ((CH3)3C-), isobutyl ((CH3)2CHCH2-) are common 4-carbon alkyl groups.

• Arenes (Aryl Groups): Aromatic ring systems acting as substituents. The most common is phenyl (C6H5- or Ph-, derived from benzene). Benzyl (C6H5CH2- or Bn-, derived from toluene) is distinct, as it includes a methylene (-CH2-) group connecting the phenyl ring to the main chain. This distinction is crucial for understanding reactivity and nomenclature.

Haloalkanes (Alkyl Halides) (In-Depth)

• Structure: Organic compounds containing at least one halogen atom (F, Cl, Br, I) covalently bonded to an alkyl group. They can be named as haloalkanes (IUPAC, e.g., chloromethane) or alkyl halides (common, e.g., methyl chloride).

• Classification (based on the carbon bearing the halogen):

  • Primary (1^ ext{o}): The carbon atom bonded to the halogen is attached to only one other carbon atom (e.g., CH3CH2Cl
    -Chloroethane).

  • Secondary (2^ ext{o}): The carbon atom bonded to the halogen is attached to two other carbon atoms (e.g., CH3CHClCH3
    -2-Chloropropane).

  • Tertiary (3^ ext{o}): The carbon atom bonded to the halogen is attached to three other carbon atoms (e.g., (CH3)3CCl
    -2-Chloro-2-methylpropane).

  • Quaternary carbons (bonded to four other carbons) cannot form halides as there are no hydrogens left to be replaced by a halogen.

• Other Halides:

  • Alkenyl Halide: Halogen is directly attached to one of the sp^2 carbons of a double bond (e.g., bromoethene). These exhibit different reactivity than alkyl halides (less reactive in substitution).

  • Aryl Halide: Halogen is directly attached to an aromatic ring (e.g., chlorobenzene). Also typically less reactive towards nucleophilic substitution compared to alkyl halides.

• Reactions: Haloalkanes are important intermediates due to their reactivity in nucleophilic substitution (SN1, SN2) and elimination (E1, E2) reactions, which lead to the formation of other functional groups.

Alcohols and Phenols (In-Depth)

• Alcohols: Organic compounds containing a hydroxyl (-OH) functional group attached to an sp^3-hybridized carbon atom. They can be considered derivatives of water (H-O-H) where one hydrogen is replaced by an alkyl group, or derivatives of alkanes where a hydrogen is replaced by an OH group.

  • Classification (based on the carbon bearing the OH group):

    • Primary Alcohol (1^ ext{o}): The carbon bearing the OH group is attached to only one other carbon atom (e.g., ethanol, benzyl alcohol).

    • Secondary Alcohol (2^ ext{o}): The carbon bearing the OH group is attached to two other carbon atoms (e.g., isopropyl alcohol, menthol).

    • Tertiary Alcohol (3^ ext{o}): The carbon bearing the OH group is attached to three other carbon atoms (e.g., tert-butyl alcohol).

  • Properties and Reactivity: Alcohols can form hydrogen bonds due to the electronegativity of oxygen, leading to higher boiling points compared to alkanes of similar molecular weight. They are weak acids (similar to water) and can act as nucleophiles or electrophiles. They undergo oxidation, dehydration, and substitution reactions.

  • Examples: Ethanol (CH3CH2OH), Geraniol (natural product).

• Phenols: Compounds where a hydroxyl (-OH) group is directly attached to an aromatic ring.

  • Acidity: Phenols are significantly more acidic than typical aliphatic alcohols (pKa ~10 vs. ~16-18) because the phenoxide ion (the conjugate base) is stabilized by resonance, with the negative charge delocalized into the aromatic ring. This increased acidity allows them to react with bases like NaOH (an aliphatic alcohol generally does not).

  • Examples: Phenol (C6H5OH), Estradiol (hormone), Tetracyclines (antibiotics containing phenolic groups).

Ethers (In-Depth)

• Structure: Ethers have the general formula R-O-R', where R and R' are alkyl or aryl groups. The oxygen atom is sp^3-hybridized and has a bent geometry, similar to water.

• Properties: Ethers are generally quite stable and relatively unreactive compared to alcohols, making them excellent solvents (e.g., diethyl ether, tetrahydrofuran - THF). They do not have hydroxyl hydrogens, so they cannot form hydrogen bonds with themselves, leading to lower boiling points than isomeric alcohols (but higher than alkanes due to dipole-dipole interactions). They can, however, act as hydrogen bond acceptors with polar protic solvents.

• Examples:

  • Dimethyl ether (CH3-O-CH3)

  • Diethyl ether (CH3CH2-O-CH2CH3)

  • Cyclic Ethers: THF (tetrahydrofuran) is a five-membered cyclic ether. Epoxides (oxiranes) are three-membered cyclic ethers, which are highly strained and thus more reactive than other ethers.

• Fluorinated Ethers: Incorporating fluorine atoms into ethers (e.g., anesthetic agents) increases their polarity due to the strong C-F dipole, and can reduce their volatility (increase boiling point) due to stronger intermolecular forces.

Amines (In-Depth)

• Structure: Amines are organic derivatives of ammonia (NH_3), where one or more hydrogen atoms are replaced by alkyl (R) or aryl groups. The nitrogen atom in amines is typically sp^3-hybridized, giving it a pyramidal geometry with a lone pair of electrons.

• Classification (based on the number of R groups attached to nitrogen):

  • Primary Amine (1^ ext{o}): Nitrogen is attached to one R group (e.g., methylamine, CH3NH2; anilines, where NH_2 is attached to an aryl group).

  • Secondary Amine (2^ ext{o}): Nitrogen is attached to two R groups and one hydrogen (e.g., dimethylamine, (CH3)2NH).

  • Tertiary Amine (3^ ext{o}): Nitrogen is attached to three R groups (e.g., trimethylamine, (CH3)3N).

  • Quaternary Ammonium Salts: If a tertiary amine is reacted with an alkyl halide, it can form a quaternary ammonium ion (R_4N^+), which is positively charged and has four R groups attached to nitrogen.

• Basicity: Amines are the most common organic bases due to the lone pair of electrons on the nitrogen atom, which can accept a proton from an acid. The basicity is influenced by the nature of the R groups (electron-donating groups increase basicity). Primary and secondary amines can also form hydrogen bonds, influencing their physical properties.

Functional Group Concepts (In-Depth)

• Definition and Classification: Functional groups are specific groupings of atoms within molecules that exhibit characteristic chemical reactions. The identity of these atoms (e.g., oxygen in alcohols, nitrogen in amines, halogens in haloalkanes) dictates the functional group and its properties. For instance, the presence of an OH group defines an alcohol, while a C=O defines a carbonyl, each with distinct reactivity patterns.

• Predicting Reactivity: Molecules with similar functional groups tend to undergo similar types of reactions, allowing for the prediction of chemical behavior. For example, all alcohols can typically undergo oxidation reactions, and compounds with C=C double bonds (alkenes) typically undergo addition reactions.

• Hybridization and Reactivity: The hybridization state of carbon atoms significantly impacts molecular geometry and reactivity. For instance:

  • Alkenes: Contain an sp^2-hybridized carbon atom participating in a carbon-carbon double bond (C=C). This double bond is a region of high electron density and acts as a nucleophile, readily undergoing addition reactions where the hybridization changes from sp^2 to sp^3. The presence of the \pi bond also allows for cis/trans isomerism.

  • Alkanes: Consist solely of sp^3-hybridized carbon atoms and single bonds (C-C and C-H). They are saturated, meaning they contain the maximum number of hydrogens, and are relatively unreactive, primarily undergoing substitution reactions (e.g., free radical halogenation) or combustion.

Hydrocarbon Families (In-Depth)

• Alkanes: Saturated hydrocarbons composed entirely of sp^3-hybridized carbon atoms and hydrogen atoms linked by single bonds. Their general formula is CnH{2n+2}. They are characterized by free rotation around their C-C single bonds, leading to various conformations (e.g., staggered, eclipsed for ethane).

  • Examples: Methane (CH4), Ethane (CH3CH3), Propane (CH3CH2CH3).

• Alkenes: Unsaturated hydrocarbons containing at least one carbon-carbon double bond (C=C). The carbons involved in the double bond are sp^2-hybridized and planar. Their general formula is CnH{2n} (for acyclic monoalkenes). The \pi bond is a source of reactivity, undergoing electrophilic addition.

  • Isomerism: Due to restricted rotation around the double bond, alkenes can exhibit cis-trans (geometric) isomerism if each carbon of the double bond is attached to two different groups.

• Cycloalkanes: Alkanes that form a closed ring structure. Their general formula is CnH{2n}, reflecting the loss of two hydrogens upon ring formation compared to an open-chain alkane.

  • Ring Strain: Small rings (cyclopropane, cyclobutane) exhibit significant angle strain due to deviation from the ideal 109.5^ ext{o} bond angles of sp^3 carbons, making them more reactive. Cyclohexane, in its chair conformation, is largely free of strain.

• Alkynes: Unsaturated hydrocarbons containing at least one carbon-carbon triple bond (C\equiv C). The carbons involved are sp-hybridized and linear. Their general formula is CnH{2n-2} (for acyclic monoalkynes). Terminal alkynes (where the triple bond is at the end of the chain, R-C\equiv C-H) are weakly acidic due to the sp hybridization of the terminal carbon, allowing for deprotonation by strong bases to form acetylide anions.

• Aromatic Compounds (Arenes): These are cyclic, planar molecules that exhibit special stability due to the delocalization of \pi electrons. Benzene (C6H6) is the quintessential example.

  • Aromaticity Criteria (Hückel's Rule): A compound is aromatic if it is cyclic, planar, fully conjugated (every atom in the ring has a p-orbital), and contains (4n+2) \pi electrons (where n is a non-negative integer). For benzene, n=1, so it has (4(1)+2)=6 \pi electrons.

  • Stability: The delocalization of \pi electrons imparts significant resonance stabilization, making aromatic compounds much more stable and less reactive towards addition reactions compared to simple alkenes. They primarily undergo electrophilic aromatic substitution reactions, retaining their aromaticity.

Benzene and Resonance (In-Depth)

• Atomic Orbitals: In benzene, each of the six carbon atoms is sp^2-hybridized, with the remaining unhybridized p-orbital on each carbon perpendicular to the plane of the ring. These six p-orbitals overlap laterally both above and below the ring, creating a continuous \pi -electron cloud.

• Resonance Hybrids: Benzene cannot be accurately represented by a single Lewis structure with alternating single and double bonds (Kekulé structures). Instead, it is best described as a resonance hybrid of two equivalent Kekulé structures. The actual structure is an average of these contributing forms.

• Bond Lengths: A key experimental observation supporting resonance in benzene is that all carbon-carbon bond lengths in the ring are identical (1.39 \mathring{A} or 0.139 \text{ nm}). This value is intermediate between a typical C-C single bond (1.54 \mathring{A}) and a typical C=C double bond (1.34 \mathring{A}), confirming the delocalized nature of the electrons.

Naming and Parent Names (In-Depth)

• IUPAC Nomenclature: Organic compounds are systematically named according to IUPAC (International Union of Pure and Applied Chemistry) rules.

  • Alkanes: The longest continuous carbon chain determines the parent name. Substituents are then numbered from the end of the chain that gives the lowest numbers to the substituents. Prefixes indicate the number of carbons:

    • 1 carbon: meth-

    • 2 carbons: eth-

    • 3 carbons: prop-

    • 4 carbons: but-

    • 5 carbons: pent-

    • …up to 10 carbons: dec- (e.g., undec- for 11, dodec- for 12).

  • Cycloalkanes: Named by adding the prefix 'cyclo-' to the alkane name corresponding to the number of carbons in the ring (e.g., cyclopropane, cyclohexane). If there are substituents, numbering starts from a substituent and proceeds around the ring to give the lowest possible numbers to other substituents.

• Common Names: Many compounds retain common or trivial names, which are important to memorize (e.g., isobutane for 2-methylpropane).

Alkyl Substituents and Arenes (In-Depth)

• Alkyl Groups: Formed by removing one hydrogen atom from an alkane. They are named by replacing the '-ane' suffix of the parent alkane with '-yl'.

  • Examples:

    • Methyl (-CH_3) from methane.

    • Ethyl (-CH2CH3) from ethane.

    • Propyl (-CH2CH2CH_3) from propane.

    • Isopropyl (CH3CH(CH3)-) from propane, attached at the middle carbon.

    • Butyl (-CH2CH2CH2CH3), sec-butyl (CH3CH(CH2CH3)-), tert-butyl ((CH3)3C-), isobutyl ((CH3)2CHCH2-) are common 4-carbon alkyl groups.

• Arenes (Aryl Groups): Aromatic ring systems acting as substituents. The most common is phenyl (C6H5- or Ph-, derived from benzene). Benzyl (C6H5CH2- or Bn-, derived from toluene) is distinct, as it includes a methylene (-CH2-) group connecting the phenyl ring to the main chain. This distinction is crucial for understanding reactivity and nomenclature.

Haloalkanes (Alkyl Halides) (In-Depth)

• Structure: Organic compounds containing at least one halogen atom (F, Cl, Br, I) covalently bonded to an alkyl group. They can be named as haloalkanes (IUPAC, e.g., chloromethane) or alkyl halides (common, e.g., methyl chloride).

• Classification (based on the carbon bearing the halogen):

  • Primary (1^ ext{o}): The carbon atom bonded to the halogen is attached to only one other carbon atom (e.g., CH3CH2Cl
    -Chloroethane).

  • Secondary (2^ ext{o}): The carbon atom bonded to the halogen is attached to two other carbon atoms (e.g., CH3CHClCH3
    -2-Chloropropane).

  • Tertiary (3^ ext{o}): The carbon atom bonded to the halogen is attached to three other carbon atoms (e.g., (CH3)3CCl
    -2-Chloro-2-methylpropane).

  • Quaternary carbons (bonded to four other carbons) cannot form halides as there are no hydrogens left to be replaced by a halogen.

• Other Halides:

  • Alkenyl Halide: Halogen is directly attached to one of the sp^2 carbons of a double bond (e.g., bromoethene). These exhibit different reactivity than alkyl halides (less reactive in substitution).

  • Aryl Halide: Halogen is directly attached to an aromatic ring (e.g., chlorobenzene). Also typically less reactive towards nucleophilic substitution compared to alkyl halides.

• Reactions: Haloalkanes are important intermediates due to their reactivity in nucleophilic substitution (SN1, SN2) and elimination (E1, E2) reactions, which lead to the formation of other functional groups.

Alcohols and Phenols (In-Depth)

• Alcohols: Organic compounds containing a hydroxyl (-OH) functional group attached to an sp^3-hybridized carbon atom. They can be considered derivatives of water (H-O-H) where one hydrogen is replaced by an alkyl group, or derivatives of alkanes where a hydrogen is replaced by an OH group.

  • Classification (based on the carbon bearing the OH group):

    • Primary Alcohol (1^ ext{o}): The carbon bearing the OH group is attached to only one other carbon atom (e.g., ethanol, benzyl alcohol).

    • Secondary Alcohol (2^ ext{o}): The carbon bearing the OH group is attached to two other carbon atoms (e.g., isopropyl alcohol, menthol).

    • Tertiary Alcohol (3^ ext{o}): The carbon bearing the OH group is attached to three other carbon atoms (e.g., tert-butyl alcohol).

  • Properties and Reactivity: Alcohols can form hydrogen bonds due to the electronegativity of oxygen, leading to higher boiling points compared to alkanes of similar molecular weight. They are weak acids (similar to water) and can act as nucleophiles or electrophiles. They undergo oxidation, dehydration, and substitution reactions.

  • Examples: Ethanol (CH3CH2OH), Geraniol (natural product).

• Phenols: Compounds where a hydroxyl (-OH) group is directly attached to an aromatic ring.

  • Acidity: Phenols are significantly more acidic than typical aliphatic alcohols (pKa ~10 vs. ~16-18) because the phenoxide ion (the conjugate base) is stabilized by resonance, with the negative charge delocalized into the aromatic ring. This increased acidity allows them to react with bases like NaOH (an aliphatic alcohol generally does not).

  • Examples: Phenol (C6H5OH), Estradiol (hormone), Tetracyclines (antibiotics containing phenolic groups).

Ethers (In-Depth)

• Structure: Ethers have the general formula R-O-R', where R and R' are alkyl or aryl groups. The oxygen atom is sp^3-hybridized and has a bent geometry, similar to water.

• Properties: Ethers are generally quite stable and relatively unreactive compared to alcohols, making them excellent solvents (e.g., diethyl ether, tetrahydrofuran - THF). They do not have hydroxyl hydrogens, so they cannot form hydrogen bonds with themselves, leading to lower boiling points than isomeric alcohols (but higher than alkanes due to dipole-dipole interactions). They can, however, act as hydrogen bond acceptors with polar protic solvents.

• Examples:

  • Dimethyl ether (CH3-O-CH3)

  • Diethyl ether (CH3CH2-O-CH2CH3)

  • Cyclic Ethers: THF (tetrahydrofuran) is a five-membered cyclic ether. Epoxides (oxiranes) are three-membered cyclic ethers, which are highly strained and thus more reactive than other ethers.

• Fluorinated Ethers: Incorporating fluorine atoms into ethers (e.g., anesthetic agents) increases their polarity due to the strong C-F dipole, and can reduce their volatility (increase boiling point) due to stronger intermolecular forces.

Amines (In-Depth)

• Structure: Amines are organic derivatives of ammonia (NH_3), where one or more hydrogen atoms are replaced by alkyl (R) or aryl groups. The nitrogen atom in amines is typically sp^3-hybridized, giving it a pyramidal geometry with a lone pair of electrons.

• Classification (based on the number of R groups attached to nitrogen):

  • Primary Amine (1^ ext{o}): Nitrogen is attached to one R group (e.g., methylamine, CH3NH2; anilines, where NH_2 is attached to an aryl group).

  • Secondary Amine (2^ ext{o}): Nitrogen is attached to two R groups and one hydrogen (e.g., dimethylamine, (CH3)2NH).

  • Tertiary Amine (3^ ext{o}): Nitrogen is attached to three R groups (e.g., trimethylamine, (CH3)3N).

  • Quaternary Ammonium Salts: If a tertiary amine is reacted with an alkyl halide, it can form a quaternary ammonium ion (R_4N^+), which is positively charged and has four R groups attached to nitrogen.

• Basicity: Amines are the most common organic bases due to the lone pair of electrons on the nitrogen atom, which can accept a proton from an acid. The basicity is influenced by the nature of the R groups (electron-donating groups increase basicity). Primary and secondary amines can also form hydrogen bonds, influencing their physical properties.