Chapter 11 Notes: Introduction to Organic Compounds and Hydrocarbons

11.1 Organic Compounds

• Organic chemistry is the study of carbon compounds. Common organic compounds contain carbon and hydrogen, e.g., vegetable oil is made of organic compounds.
• Goal: Identify properties characteristic of organic or inorganic compounds.
• An organic compound:
  • is a compound made from carbon and hydrogen atoms
  • may also contain other nonmetals such as O, S, N, P, or halogens (F, Cl, Br, I)
  • is often found in products like gasoline, medicines, shampoos, plastics, and perfumes
• Formula conventions:
  • Formulas are written with carbon first, then hydrogen, then other elements.
• Key ideas:
  • Organic compounds typically have covalent bonds, low melting/boiling points, are flammable and undergo combustion, and are not soluble in water.
  • Example: Vegetable oil is a mixture of organic compounds and is not soluble in water.
• Properties of inorganic compounds (contrast):
  • Often have ionic bonds, high melting/boiling points, usually soluble in water, most do not burn in air.
  • Example: Salt, NaCl, is inorganic and composed of Na⁺ and Cl⁻ ions.
• Quick check question examples:
  • Identify features typical of organic vs inorganic compounds.

11.2 Hydrocarbons and Bonding Basics

• Hydrocarbons are organic compounds that contain only carbon and hydrogen.
• HONC 1234 rule (a quick way to remember bonding): Hydrogen, Oxygen, Nitrogen, Carbon, Carbon forms four bonds (H and O are often single, N can make three bonds with a lone pair, etc.).
• In organic molecules, every carbon atom has four bonds.
• Saturated hydrocarbons contain only single bonds. Examples: methane (CH₄), ethane (C₂H₆), propane (C₃H₈), butane (C₄H₁₀).
• Common hydrocarbon examples and representations of methane (CH₄):
  • 2D/3D representations; note tetrahedral geometry with bond angles ≈ 109.5°.
  • Example formula: ext{CH}_4
    ightarrow ext{tetrahedral geometry}, heta o 109^ ext{o}
• Ethane (C₂H₆): each carbon forms three C–H bonds and one C–C bond; in a Newman-like view, the C–C bond allows rotation (single bond).
• Methane and ethane illustrations include space-filling, ball-and-stick, wedge-dash, expanded and condensed structural formulas.
• Learning check reminder: In butane, C₄H₁₀, predict the shape around each carbon (sp³, tetrahedral around each carbon).

11.2 Alkanes (Intro to the IUPAC system)

• Alkanes are hydrocarbons with only C–C and C–H bonds.
• They are formed by a continuous chain of carbon atoms.
• Naming: IUPAC system; endings -ane; Greek prefixes for carbon chains with five or more carbons.
• Key concepts:
  • Condensed structural formula: each carbon and its attached hydrogens written as a group; a subscript indicates hydrogens bonded to each carbon.
  • Expanded structural formula: shows all bonds.
  • Skeletal (line-angle) formula: carbon skeleton with carbon atoms at line ends or intersections; hydrogen atoms implied to satisfy valence.
  • Molecular formula: gives total C and H in the molecule.
• Examples:
  • Butane: condensed formula $ext{CH}<em>3 ext{-CH}</em>2 ext{-CH}<em>2 ext{-CH}</em>3$
  • Large alkanes: C₆H₁₄ (hexane), C₈H₁₈ (octane), etc.
• IUPAC rules overview:
  • Endings: -ane
  • Use Greek prefixes for chains with five or more carbons
• IUPAC naming steps (overview):
  1) Identify the longest carbon chain.
  2) Number the chain from the end nearer the first substituent.
  3) Name substituents in alphabetical order with appropriate prefixes and numbers.

11.3 Alkanes with Substituents (Branched alkanes)

• When four or more carbon atoms are present, branches (substituents) can attach to the main chain.
• Substituents include:
  • Alkyl groups: carbon groups attached to chains; named with an -yl ending (e.g., methyl, ethyl, propyl).
  • Halo substituents: halogens attached to the chain; named as fluoro-, chloro-, bromo-, iodo-.
• Structural isomers: compounds with the same molecular formula but different connectivity.
  • Example: butane (C₄H₁₀) has two structural isomers: n-butane (straight chain) and isobutane (branched).
• Naming cycloalkanes with substituents:
  • When a substituent is present on a cycloalkane, prefix the substituent name before the cycloalkane name.
  • If only a single substituent, no number is necessary.
• Examples:
  • Ethylcyclohexane: cycloalkane with an ethyl substituent on cyclohexane.
• Practice: given a line-angle formula, derive condensed formula and IUPAC name.

11.4 Properties of Alkanes

• Physical properties drive uses:
  • Gases at room temperature: C₁–C₄ (methane, ethane, propane, butane).
  • Highly volatile liquids with 5–8 carbons: pentane, hexane, heptane, octane.
  • Liquids with 9–17 carbons: in motor oils, mineral oil, kerosene, diesel, jet fuels (e.g., decane, C₁₀H₂₂).
  • 18+ carbons: waxy solids at room temperature (paraffins); petroleum jelly (Vaseline) is a semisolid mixture of hydrocarbons with >25 carbons.
• Solubility and density:
  • Alkanes are nonpolar and insoluble in water.
  • Less dense than water and flammable in air.
  • In crude oil, alkanes form a surface layer that does not mix with water (oil spills).
• Combustion of alkanes:
  • Complete combustion: alkane + O₂ → CO₂ + H₂O + energy
  • General balanced equation for methane:
    ext{CH}4(g) + 2 ext{O}2(g)
    ightarrow ext{CO}2(g) + 2 ext{H}2O(g) + ext{energy}
  • Balancing steps: (1) balance carbons, (2) balance hydrogens, (3) balance oxygens.
• Example: complete combustion of butane:
  2 ext{C}4 ext{H}{10}(g) + 13 ext{O}2(g) ightarrow 8 ext{CO}2(g) + 10 ext{H}_2O(g) + ext{energy}

11.5 Alkenes and Alkynes (Unsaturated hydrocarbons)

• Alkenes contain at least one C=C double bond; alkynes contain at least one C≡C triple bond.
• They are unsaturated hydrocarbons because they do not contain the maximum number of hydrogen atoms.
• They react with hydrogen gas to increase the hydrogen content, converting to alkanes if fully hydrogenated.
• Ethyne (acetylene) is a key example of an alkyne (C₂H₂).
• General notes:
  • Double bonds restrict rotation, leading to geometric (cis–trans) isomerism in certain cases.
  • Alkenes/alkynes can undergo addition reactions (e.g., hydrogenation, hydration).

11.6 Cis–Trans Isomers

• Double bonds are rigid and do not rotate, allowing cis–trans isomerism when two different groups are attached to each carbon of the C=C bond.
• Cis isomer: similar groups on the same side of the double bond; trans isomer: on opposite sides.
• Physical and chemical properties differ between cis and trans isomers.
• Example naming convention: prefix cis- or trans- precedes the alkene name (e.g., cis-1,2-dibromoethene, trans-1,2-dibromoethene).
• For alkenes with more than one substituent, choose定位 the appropriate orientation and use the prefix accordingly.

11.7 Addition Reactions of Alkenes and Alkynes

• Alkenes and alkynes are highly reactive at C=C and C≡C bonds; addition reactions add H–H or H–X across the multiple bond.
• Hydration: addition of water (H–OH) across a C=C to form an alcohol; catalyzed by a strong acid (e.g., H₂SO₄).
• Hydrogenation: addition of H₂ across a C=C (or C≡C) to form an alkane; often uses a catalyst such as Pt, Ni, or Pd.
• General examples:
  • Hydrogenation (alkene): ext{R-CH=CH}2 + ext{H}2
    ightarrow ext{R-CH}2-CH3 (with a Pt catalyst).
  • Hydration (alkene): ext{R-CH=CH}2 + ext{H}2 ext{O}
    ightarrow ext{R-CH(OH)-CH}_3 (acid-catalyzed; Markovnikov orientation).
• Industrial relevance: hydrogenation used to convert liquid vegetable oils to solid fats (margarine, shortening).
• Example problems in class involve drawing line-angle formulas for products and balancing hydrogenation equations.

11.8 Aromatic Compounds

• Benzene (Faraday discovered in 1825) has formula $ext{C}<em>6 ext{H}</em>6$ and a six-member ring with alternating double bonds.
• Bonding in benzene is described by two resonance structures with delocalized electrons; commonly depicted as a cyclohexene ring with a circle in the center to indicate equal bond order.
• Aromatic compounds contain a benzene ring and one or more substituents. Common benzene derivatives include:
  • Toluene (methylbenzene)
  • Aniline (aminobenzene)
  • Phenol (hydroxybenzene)
• IUPAC naming approach for benzene derivatives:
  • With one substituent, the ring is not numbered (e.g., toluene).
  • With multiple substituents, assign numbers to give the lowest possible locants and name substituents in alphabetical order, using an appropriate prefix (di-, tri-, etc.).
• TNT example: trinitrotoluene is a well-known benzene derivative.
• Common aromatic compounds are used in drugs, dyes, flavorings, and explosives, illustrating the practical significance of aromatic chemistry.

Practice and Problem-Solving Highlights (Summary of Types Covered)

• Identify whether a given compound is organic vs inorganic based on bonding and composition.
• Determine whether a hydrocarbon is saturated or unsaturated; identify alkanes, alkenes, and alkynes from formulas and structures.
• Name alkanes, cycloalkanes, and alkenes/alkynes using IUPAC conventions; recognize common substituents (alkyl and halo groups).
• Draw multiple representations of alkanes: expanded, condensed, skeletal formulas, and line-angle formulas.
• Predict products and write balanced equations for:
  • Combustion of alkanes (e.g., CH₄, C₄H₁₀): balanced equations with CO₂ and H₂O.
  • Hydrogenation of alkenes (addition of H₂) with a metal catalyst.
  • Hydration of alkenes (addition of H₂O) with acid catalysis to form alcohols.
• Identify cis–trans isomers for alkenes and name them accordingly.
• Describe the structure and bonding in benzene and name aromatic compounds; understand circle representation and resonance.

Key Formulas and Equations (LaTeX)

• General alkane formula (universal for acyclic alkanes): $ext{C}<em>n ext{H}</em>{2n+2}$
• Methane: $ext{CH}<em>4$; Ethane: $ext{C}</em>2 ext{H}<em>6$; Butane: $ext{C}</em>4 ext{H}<em>{10}$; Hexane: $ext{C}</em>6 ext{H}<em>{14}$; Octane: $ext{C}</em>8 ext{H}_{18}$
• Methane bond angle: heta
  ightarrow 109^ ext{o}
• Combustion of methane: ext{CH}4(g) + 2 ext{O}2(g)
  ightarrow ext{CO}2(g) + 2 ext{H}2O(g) + ext{energy}
• Combustion of butane: 2 ext{C}4 ext{H}{10}(g) + 13 ext{O}2(g) ightarrow 8 ext{CO}2(g) + 10 ext{H}_2O(g) + ext{energy}
• Hydrogenation of an alkene: ext{R-CH=CH}2 + ext{H}2
  ightarrow ext{R-CH}2-CH3 ext{ (Pt catalyst)}
• Hydration of an alkene (acid-catalyzed): ext{R-CH=CH}2 + ext{H}2 ext{O}
  ightarrow ext{R-CH(OH)-CH}3 ext{ (H}2 ext{SO}_4 ext{)}
• Benzene: $ext{C}<em>6 ext{H}</em>6$

Quick Reference Concepts to Memorize

• Organic vs inorganic: covalent vs ionic bonds, solubility, boiling/melting points, flammability.
• HONC 1234: Carbon forms four bonds; H, O, N, C are central to bonding patterns.
• Alkane generics: saturated hydrocarbons with only single bonds; formula pattern $ext{C}<em>n ext{H}</em>{2n+2}$ for acyclic alkanes.
• Alkanes with substituents: alkyl groups (-yl) and halogen substituents (fluoro-, chloro-, bromo-, iodo-).
• Cycloalkanes: ring structures with two fewer hydrogens than the open chain; general formula $ext{C}<em>n ext{H}</em>{2n}$ for cycloalkanes.
• Alkenes vs alkynes: C=C double bonds vs C≡C triple bonds; unsaturated and undergo addition reactions.
• Cis–trans isomerism arises when two different groups are attached to each carbon of a C=C bond.
• Aromatic compounds: benzene ring with delocalized electrons; resonance; circle representation.
• Practical implications: hydrogenation used to convert oils to fats; aromatic compounds have real-world applications and reactivity patterns.