Exhaustive Organic Chemistry Study Guide and IUPAC Nomenclature Manual

Foundations of Organic Chemistry and Molecular Representation

• Definition of Organic Chemistry: The study of hydrocarbons and their derivatives.
• Definition of Hydrocarbons: Compounds composed exclusively of Carbons and Hydrogens.
  • Examples include Alkanes such as ethane ($CH_3-CH_3$), propane ($CH_3-CH_2-CH_3$), and butane ($CH_3-CH_2-CH_2-CH_3$).
• Homologous Series: A series of compounds sharing the same functional group where consecutive members differ by a $-CH_2-$ unit.
• Wohler Synthesis: The laboratory synthesis of urea from an inorganic precursor:
  • $NH_4NCO \text{ (ammonium cyanate)} \rightarrow NH_2CONH_2 \text{ (urea)}$

Molecular Formulas and Structural Representations

Organic molecules are represented through various structural formulas:

• Dash Formula: Shows every bond explicitly (e.g., all H-C and C-C bonds).
• Condensed Formula: Groups atoms together without showing every bond (e.g., $CH_3(CH_2)_2CH_3$).
• Bond Line Formula: Uses lines where vertices and ends represent carbon atoms; hydrogens attached to carbons are implied to satisfy carbon's tetravalency.

Calculation of Sigma ($\sigma$) and Pi ($\pi$) Bonds

• Single bonds consist of one $\sigma$ bond.
• Double bonds consist of one $\sigma$ and one $\pi$ bond.
• Triple bonds consist of one $\sigma$ and two $\pi$ bonds.

Specific Molecule Calculations:

• Ethane ($CH_3-CH_3$): $7\sigma, 0\pi$
• Ethene ($CH_2=CH_2$): $5\sigma, 1\pi$
• Ethyne ($H-C \equiv C-H$): $3\sigma, 2\pi$
• $CH_3-C \equiv C-CH_3$: $9\sigma, 2\pi$
• $H-C \equiv N$: $2\sigma, 2\pi$
• Buta-1,3-diene ($CH_2=CH-CH=CH_2$): $9\sigma, 2\pi$
• Benzene ($C_6H_6$): $12\sigma, 3\pi$
• $N \equiv C-C \equiv N$: $3\sigma, 4\pi$
• $H-C \equiv C-CH=CH_2$: $7\sigma, 3\pi$

Degrees of Carbon and Hydrogen

Degrees of carbons are determined by the number of other carbons directly attached to the atom in question:

• $1^\circ$ (Primary Carbon): Carbon directly attached to one other carbon.
• $2^\circ$ (Secondary Carbon): Carbon directly attached to two other carbons.
• $3^\circ$ (Tertiary Carbon): Carbon directly attached to three other carbons.
• $4^\circ$ (Quaternary Carbon): Carbon directly attached to four other carbons.

Degrees of Hydrogen:

• Positions follow the carbon they are attached to:
  • $1^\circ$ Hydrogen: Attached to a $1^\circ$ carbon.
  • $2^\circ$ Hydrogen: Attached to a $2^\circ$ carbon.
  • $3^\circ$ Hydrogen: Attached to a $3^\circ$ carbon.
  • Note: Quaternary carbons cannot have hydrogens attached.

Example Analysis (Isooctane):

• Structure: $CH_3 - C(CH_3)_2 - CH_2 - CH(CH_3) - CH_3$
• $1^\circ$ Carbons: 5
• $2^\circ$ Carbons: 1
• $3^\circ$ Carbons: 1
• $4^\circ$ Carbons: 1
• $1^\circ$ Hydrogens: 15
• $2^\circ$ Hydrogens: 2
• $3^\circ$ Hydrogens: 1

Degree of Alcohols, Halides, and Amines

Alcohol Degree ($R-OH$):

• The degree of the alcohol is equal to the degree of the carbon to which the $-OH$ group is directly attached.
  • $1^\circ$ Alcohol: $-OH$ attached to a primary carbon.
  • $2^\circ$ Alcohol: $-OH$ attached to a secondary carbon.
  • $3^\circ$ Alcohol: $-OH$ attached to a tertiary carbon.

Halide Degree ($R-X$):

• Identical to alcohols; based on the degree of the carbon attached to the halogen ($F, Cl, Br, I$).

Amine Degree:

• Based on the number of carbon atoms directly attached to the nitrogen ($N$) atom, rather than the degree of the carbon itself.
  • $1^\circ$ Amine (Primary): One carbon attached to $N$ ($R-NH_2$).
  • $2^\circ$ Amine (Secondary): Two carbons attached to $N$ ($R-NH-R$).
  • $3^\circ$ Amine (Tertiary): Three carbons attached to $N$ ($R-N(R)-R$).

Functional Groups Overview

A functional group is an atom or group of atoms where the majority of chemical reactions occur.

Common Functional Groups:

• Alcohol: $R-OH$
• Ether: $R-O-R$
• Aldehyde: $R-CHO$ (Lowest mass: Methanal/Formaldehyde, $H-CHO$
• Ketone: $R-CO-R$ (Lowest mass: Propanone/Acetone, $CH_3COCH_3$)
• Carboxylic Acid: $R-COOH$ (Lowest mass: Methanoic acid/Formic acid, $H-COOH$)
• Cyanide (Nitrile): $R-C \equiv N$
• Isocyanide: $R-N \equiv C$
• Acid Halide: $R-CO-X$
• Ester: $R-CO-OR$
• Amide: $R-CONH_2$
• Acid Anhydride: $R-CO-O-CO-R$
• Thiol: $R-SH$
• Thio Ester: $R-CO-SR$
• Nitro: $R-NO_2$
• Nitroso: $R-N=O$
• Azido: $R-N_3$
• Imine: $>C=N-H$

Degree of Unsaturation (DU) / Double Bond Equivalent (DBE)

Degree of Unsaturation represents the index of hydrogen deficiency ($IHD$). It indicates the number of rings or pi bonds in a molecule.

Mathematical Formula:$DBE = (C + 1) - \frac{H + X - N}{2}$ Where:

• $C$ = Number of Carbon atoms
• $H$ = Number of Hydrogen atoms
• $X$ = Number of Halogen atoms ($F, Cl, Br, I$)
• $N$ = Number of Nitrogen atoms

Valuations:

• Double Bond = 1 DU
• Triple Bond = 2 DU
• Ring = 1 DU
• Benzene ring = 4 DU (1 ring + 3 pi bonds)

Example Calculations:

• $C_4H_{10}$: $DBE = (4+1) - (10/2) = 0$
• $C_3H_6$: $DBE = (3+1) - (6/2) = 1$
• $C_4H_6$: $DBE = (4+1) - (6/2) = 2$
• $C_{10}H_{20}$: $DBE = (10+1) - (20/2) = 1$
• $C_6H_6$: $DBE = (6+1) - (6/2) = 4$
• $C_2H_4O_2$: $DBE = (2+1) - (4/2) = 1$

Classification of Organic Compounds

1. Acyclic (Open Chain):
   • Saturated: Alkanes ($C_nH_{2n+2}$), also known as Paraffins.
   • Unsaturated: Alkenes ($C_nH_{2n}$ / Olefins) and Alkynes ($C_nH_{2n-2}$).
2. Cyclic (Closed Chain):
   • Homocyclic: Ring contains only carbon atoms.
     • Alicyclic: Behave like aliphatic compounds (e.g., Cyclohexane).
     • Aromatic: Contain a delocalized system of pi electrons.
       • Benzenoid: Contain a benzene ring (e.g., Benzene, Naphthalene).
       • Non-Benzenoid: Aromatic but lacks a benzene ring (e.g., Tropone, Tropolone).
   • Heterocyclic: Ring contains an atom other than carbon (e.g., Pyrrole, Furan, Thiophene, Pyridine).

IUPAC Nomenclature Framework

IUPAC names consist of five distinct components: [Secondary Prefix] + [Primary Prefix] + [Word Root] + [Primary Suffix] + [Secondary Suffix]

1. Secondary Prefix ($2^\circ$): Denotes substituents (locants + substituent name).
2. Primary Prefix ($1^\circ$): Indicates if the molecule is cyclic ($cyclo$, $bicyclo$, $spiro$).
3. Word Root: Indicates the number of carbons in the principal chain:
   • $C_1$: meth
   • $C_2$: eth
   • $C_3$: prop
   • $C_4$: but
   • $C_5$: pent
   • $C_6$: hex
   • $C_7$: hept
   • $C_8$: oct
   • $C_9$: non
   • $C_{10}$: dec
   • $C_{11}$: undec
   • $C_{12}$: dodec
4. Primary Suffix ($1^\circ$): Indicates saturation/unsaturation:
   • Saturated: $ane$
   • Double bond: $ene$ ($diene$ for 2, $triene$ for 3)
   • Triple bond: $yne$ ($diyne$ for 2)
5. Secondary Suffix ($2^\circ$): Denotes the principal functional group (e.g., $ol$ for alcohol, $al$ for aldehyde).

Rules for Substituents and Numbering

• Selection of Principal Chain: Select the longest continuous carbon chain containing the maximum number of multiple bonds and functional groups.
  • If two chains are the same length, choose the one with the maximum number of substituents.
• Lowest Possible Number Rule (LPN): Number the chain from the end that gives substituents the lowest possible locants.
• Alphabetical Order: Substituents must be written in alphabetical order in the final name.
  • Note: Di, Tri, Tetra, Sec, and Tert are not considered for alphabetical ordering, but Iso, Neo, and Cyclo are included.
• Tie-breaking: If numbering from both ends yields the same locant set, use alphabetical priority of substituents.

IUPAC Nomenclature for Alkenes and Alkynes

• Priority: Multiple bonds ($C=C$ and $C \equiv C$) take priority over alkyl substituents in numbering.
• Rule for Ene-Yne: If a double bond and a triple bond are at equidistant positions, the double bond gets the lower number. In naming, the nomenclature follows the format: "Wordroot-x-en-y-yne" (the 'e' of 'ene' is dropped because it is followed by 'y').
• Alkenyl groups: $-CH=CH_2$ (Ethenyl/Vinyl), $-CH_2-CH=CH_2$ (Prop-2-enyl/Allyl).
• Alkylidene groups: $=CH_2$ (Methylidene), $=CH-CH_3$ (Ethylidene).

Specific Functional Group Suffixes and Prefixes

Special Suffixes for Cyclic and Polyfunctional Systems

When a functional group carbon is directly attached to a ring or when there are three or more identical groups attached to an unbranched chain (1993 IUPAC rule update), special suffixes are used:

• Carboxylic acid: Carboxylic acid (instead of oic acid)
• Aldehyde: Carbaldehyde (instead of al)
• Nitrile: Carbonitrile (instead of nitrile)
• Acid Chloride: Carbonoyl chloride
• Ester: Carboxylate

Example: Cyclopropane carboxylic acid (a carboxyl group on a three-membered ring).

Priority Table for Polyfunctional Groups

When multiple functional groups are present, priority determines the secondary suffix (principal group); all others become prefixes. Priority Order (Highest to Lowest):

1. Carboxylic Acid
2. Sulphonic Acid
3. Acid Anhydride
4. Ester
5. Acid Halide
6. Amide
7. Nitrile
8. Isocyanide
9. Aldehyde
10. Ketone
11. Alcohol
12. Thiol
13. Amine
14. Alkene / Alkyne

Nomenclature of Aromatic Compounds

• Benzene derivatives: Use "benzene" as the parent word root.
• Common names accepted by IUPAC:
  • Methyl benzene: Toluene
  • Hydroxy benzene: Phenol
  • Amino benzene: Aniline
  • Methoxy benzene: Anisole
  • Benzene carbaldehyde: Benzaldehyde
  • Benzene carboxylic acid: Benzoic acid
  • Ethenyl benzene: Styrene
• Positional isomers:
  • 1,2-disubstitution = Ortho (o-)
  • 1,3-disubstitution = Meta (m-)
  • 1,4-disubstitution = Para (p-)

Physical and Chemical Data Tables

Melting and Boiling Points of Alkanes:

• Methane ($CH_4$): bp $111.0\,K$, mp $90.5\,K$
• Ethane ($C_2H_6$): bp $184.4\,K$, mp $101.0\,K$
• Propane ($C_3H_8$): bp $230.9\,K$, mp $85.3\,K$
• Butane ($C_4H_{10}$): bp $272.4\,K$, mp $134.6\,K$
• n-Octane ($C_8H_{18}$): bp $398.7\,K$, mp $216.2\,K$
• n-Decane ($C_{10}H_{22}$): bp $447.1\,K$, mp $243.3\,K$

Acidity ($pK_a$ values) of Phenols:

• Phenol: $10.0$
• o-Nitrophenol: $7.2$
• m-Nitrophenol: $8.3$
• p-Nitrophenol: $7.1$
• Ethanol: $15.9$

Basicity ($pK_b$ values) of Amines in Aqueous Phase:

• Methanamine: $3.38$
• N-Methylmethanamine: $3.27$
• Ethanamine: $3.29$
• Benzenamine (Aniline): $9.38$
• Phenylmethanamine (Benzylamine): $4.70$

Questions & Discussion

Q: What is the degree of hydrogen in isooctane?A: Isooctane ($2,2,4-trimethylpentane$) contains 15 primary ($1^\circ$) hydrogens, 2 secondary ($2^\circ$) hydrogens, and 1 tertiary ($3^\circ$) hydrogen.

Q: How do you identify a 3-degree amine?A: In a tertiary ($3^\circ$) amine, the nitrogen atom is bonded to three carbon atoms, having the general structure $R_3N$.

Q: What is the DBE of Benzene?A: Benzene has a DBE of 4, composed of one ring and three double bonds.