Introduction to Organic Chemistry Practice Flashcards

Introduction to Organic Chemistry and Molecules

• Organic chemistry is defined as the chemistry of carbon-based molecules.
• Organic molecules are molecules that are carbon-based.
• Organic chemicals are prevalent in various fields and substances, including:
  • DNA
  • Materials
  • Essential oils
  • PIR
  • Medicines, which consist of:
  • Active Pharmaceutical Ingredients (APIs)
  • Excipients
  • Fuels
  • Pigments

Properties of Organic Molecules

• Organic molecules possess specific properties that define their behavior and stability:
  • Stability: They are composed of stable $C-C$ covalent bonds.
  • Defined molecular structures.
  • Defined three-dimensional shapes.

Basic Structure of Carbon

• Carbon atoms form four single covalent bonds.
• The molecular shape formed by these four bonds is tetrahedral.
• A single bond is composed of $2$ electrons.
• Example: Methane ($CH_4$).
  • Carbon ($C$) is at the center bonded to four Hydrogen ($H$) atoms.

Alkanes: Saturated Hydrocarbons

• Hydrocarbons are molecules composed entirely of carbon and hydrogen.
• In these molecules, each carbon atom forms exactly $4$ chemical bonds.
• A saturated hydrocarbon is one where all $C-C$ bonds are single bonds and the molecule contains the maximum possible number of Hydrogen atoms.
• Saturated hydrocarbons are specifically called ALKANES.

Alkane Nomenclature: Prefixes and Names

• The name of an alkane is determined by the number of carbons in the chain using specific prefixes and the suffix "-ane":
  • $1$ Carbon: Meth… (e.g., Methane, $CH_4$)
  • $2$ Carbons: Eth… (e.g., Ethane, $C_2H_6$)
  • $3$ Carbons: Prop… (e.g., Propane, $C_3H_8$)
  • $4$ Carbons: But… (e.g., Butane, $C_4H_{10}$, condensed: $CH_3CH_2CH_2CH_3$)
  • $5$ Carbons: Pent… (e.g., Pentane, $C_5H_{12}$, condensed: $CH_3CH_2CH_2CH_2CH_3$)
  • $6$ Carbons: Hex… (e.g., Hexane, $C_6H_{14}$, condensed: $CH_3(CH_2)_4CH_3$)
  • $7$ Carbons: Hept… (e.g., Heptane, $C_7H_{16}$, condensed: $CH_3(CH_2)_5CH_3$)
  • $8$ Carbons: Oct… (e.g., Octane, $C_8H_{18}$, condensed: $CH_3(CH_2)_6CH_3$)
  • $9$ Carbons: Non… (e.g., Nonane, $C_9H_{20}$, condensed: $CH_3(CH_2)_7CH_3$)
  • $10$ Carbons: Dec… (e.g., Decane, $C_{10}H_{22}$, condensed: $CH_3(CH_2)_8CH_3$)
  • $11$ Carbons: Undec… (e.g., Undecane, $C_{11}H_{24}$, condensed: $CH_3(CH_2)_9CH_3$)
  • $12$ Carbons: Dodec… (e.g., Dodecane, $C_{12}H_{26}$, condensed: $CH_3(CH_2)_{10}CH_3$)

Normal vs. Branched Alkanes

• Normal alkanes (n-alkanes) consist of continuous, unweighted chains of carbon atoms.
• Branched alkanes are alkanes that are not continuous chains; they contains branches coming off a main chain.
• The longest continuous chain of carbons in any alkane is called the parent chain.

Structural Isomerism

• Structural isomers are molecules with the same chemical formulas but different molecular structures resulting from different "connectivity."
• These arise due to the multiple ways branched hydrocarbons can be formed.
• Example: Pentane ($C_5H_{12}$)
  • n-pentane: A straight chain of five carbons ($CH_3CH_2CH_2CH_2CH_3$).
  • 2-methylbutane: A four-carbon chain with a methyl branch on the second carbon ($CH_3CH_2CH(CH_3)CH_3$).

IUPAC Rules for Naming Branched Alkanes

• Rule 1: Find and name the parent chain. This is the chain containing the largest number of Carbon atoms.
• Rule 2: Number the carbon atoms in the parent chain. Start numbering from the end closest to any branching.
• Rule 3: Name alkane branches (substituents) by dropping the "-ane" suffix and adding "-yl."
  • A one-carbon branch is methyl ($-CH_3$).
  • A two-carbon branch is ethyl ($-CH_2CH_3$).
• Rule 4: Name halogen branches by dropping the "-ine" and adding "-o."
  • Example: Bromine becomes Bromo-; Chlorine becomes Chloro-.
• Rule 5: Alphabetical ordering. When different types of branches exist (e.g., ethyl and methyl), they are named in alphabetical order.
• Rule 6: Use prefixes to indicate multiple identical branches. Use "di-" for two, "tri-" for three, etc.
• Note: Every substituent must have a number indicating its position on the chain.

Alkyl Groups Reference Table

• Methane ($CH_4$) becomes a Methyl group ($CH_3-$).
• Ethane ($C_2H_6$) becomes an Ethyl group ($CH_3CH_2-$).
• Propane ($C_3H_8$) becomes a Propyl group ($CH_3CH_2CH_2-$).
• Butane ($C_4H_{10}$) becomes a Butyl group ($CH_3CH_2CH_2CH_2-$).

Naming Practice and Examples

• Example: 2-Methylpentane
  • Parent chain: Pentane ($5$ carbons).
  • Branch: Methyl ($1$ carbon) on the second carbon.
  • Incorrect naming: 4-methylpentane (numbering must start from the end closest to the branch).
• Example: 3-Methylhexane
  • Parent chain: Hexane ($6$ carbons).
  • Branch: Methyl on the third carbon.
  • Note: This is usually written as $CH_3CH_2CH(CH_3)CH_2CH_2CH_3$.
• Example: 2,2-Dimethylbutane
  • Parent chain: Butane ($4$ carbons).
  • Branches: Two methyl groups, both on the second carbon.
  • Note: Each substituent requires its own number (2,2-).
• Example: 3-Bromo-1-chlorobutane
  • Parent chain: Butane ($4$ carbons).
  • Substituents: Bromine on carbon $3$, Chlorine on carbon $1$.
  • Naming logic: Number from the end closest to the first substituent. Alphabetize the substituents regardless of position (Bromo before Chloro).
• Example: 2,2-Dimethylpentane
  • Root "pentane" = $5$ carbons in the parent chain ($CH_3CH_2CH_2CH_2CH_3$).
  • "Dimethyl" = Two methyl branches.
  • "2,2-" = Both branches on the second carbon.
• Example: 3-Ethyl-2,4-dimethylheptane
  • Root "heptane" = $7$ carbons.
  • "2,4-dimethyl" = Methyl branches on carbons $2$ and $4$.
  • "3-ethyl" = Two-carbon branch on carbon $3$.
• Example: 2,3,3-Trimethyl-4-propyloctane
  • Root "octane" = $8$ carbons.
  • "2,3,3-trimethyl" = Three methyl branches (one on carbon $2$, two on carbon $3$).
  • "4-propyl" = Three-carbon branch on carbon $4$.
• Example: 5-Ethyl-3,4-dimethyloctane
  • Root "octane" = $8$ carbons.
  • Two methyl branches at carbons $3$ and $4$.
  • One ethyl branch at carbon $5$.
  • Alphabetize: Ethyl before Methyl.

Cycloalkanes

• A cycloalkane is a hydrocarbon chain joined to form a ring.
• Formation of a ring results in the loss of two Hydrogen atoms compared to the straight-chain alkane equivalent.
• Cyclopropane ($C_3H_6$):
  • Bond angle: $60^\circ$.
  • Note: Highly unstable due to angle strain.
• Cyclobutane ($C_4H_8$):
  • Bond angle: Approximately $90^\circ$.
• Cyclopentane ($C_5H_{10}$):
  • Bond angle: Approximately $109.5^\circ$.
• Cyclohexane ($C_6H_{12}$):
  • Bond angle: $109.5^\circ$.
• Angle (Ring) Strain:
  • Occurs due to the compression of internal bond angles.
  • Cyclopropane has the greatest angle strain.
  • Strain is effectively eliminated in cyclohexane.

Alkenes and Alkynes

• Alkenes are hydrocarbons containing at least one carbon-carbon double bond ($C=C$).
• Alkynes are hydrocarbons containing at least one carbon-carbon triple bond ($C\equiv C$).
• Nomenclature:
  • Suffix changes from "-ane" to "-ene" for double bonds.
  • Suffix changes from "-ane" to "-yne" for triple bonds.
  • Numbering: Carbon chain numbering starts at the end closest to the multiple bond.

General Formulas and Homologous Series

• Alkanes: $C_nH_{2n+2}$
  • Methane ($CH_4$), Ethane ($C_2H_6$), Propane ($C_3H_8$), Butane ($C_4H_{10}$), Pentane ($C_5H_{12}$), Hexane ($C_6H_{14}$), Heptane ($C_7H_{16}$), Octane ($C_8H_{18}$), Nonane ($C_9H_{20}$), Decane ($C_{10}H_{22}$).
• Alkenes: $C_nH_{2n}$
  • Ethene ($C_2H_4$), Propene ($C_3H_6$), Butene ($C_4H_8$), Pentene ($C_5H_{10}$), Hexene ($C_6H_{12}$), Heptene ($C_7H_{14}$), Octene ($C_8H_{16}$), Nonene ($C_9H_{18}$), Decene ($C_{10}H_{20}$).
• Alkynes: $C_nH_{2n-2}$
  • Ethyne ($C_2H_2$), Propyne ($C_3H_4$), Butyne ($C_4H_6$), Pentyne ($C_5H_8$), Hexyne ($C_6H_{10}$), Heptyne ($C_7H_{12}$), Octyne ($C_8H_{14}$), Nonyne ($C_9H_{16}$), Decyne ($C_{10}H_{18}$).

Alkene/Alkyne Example Molecules

• Ethene: $H_2C=CH_2$
• Ethyne: $HC\equiv CH$
• Propene: $H_2C=CHCH_3$
• Propyne: $HC\equiv CCH_3$
• 1-Butene: $H_2C=CHCH_2CH_3$
• 2-Pentyne: $CH_3C\equiv CCH_2CH_3$
• 4-Methyl-2-pentene: A $5$-carbon chain with a double bond between C2 and C3 and a methyl group on C4.
• 2-Methyl-2-hexene: A $6$-carbon chain with a double bond on C2 and a methyl on C2.
• Cyclopentene: A five-membered ring containing one double bond.
• 2-Bromo-3-methyl-2-pentene: A $5$-carbon chain with a double bond starting at C2, bromine at C2, and methyl at C3.

Cis-Trans Isomerism

• Alkenes and alkynes show restricted rotation around multiple bonds.
• Because of the $120^\circ$ bond angles in alkenes, cis-trans isomerism is possible.
• Definitions:
  • Cis: Substituents are on the same side of the double bond.
  • Trans: Substituents are on opposite sides of the double bond.
• Constraints: If one of the carbons in the double bond has two identical substituents, cis-trans isomerism is NOT possible.
• Prioritization: Molar mass is used to prioritize substituents to determine isomerism.
• Examples using 2-Butene ($C_4H_8$):
  • Cis-2-butene: Both methyl groups are on the same side of the $C=C$.
  • Trans-2-butene: Methyl groups are on opposite sides of the $C=C$.