Chemistry 122 Introductory Organic Chemistry Fall Quarter 2015 Dr. Thomas H. Schultz What is Organic chemistry? What is Organic chemistry? The study of carbon and its compounds. What is Organic chemistry? The study of carbon and its compounds. First we will talk about compounds just containing carbon and hydrogen, these compounds are called hydrocarbons. What is Organic chemistry? The study of carbon and its compounds. First we will concentrate on compounds just containing carbon and hydrogen, these compounds are called hydrocarbons. Hydrocarbon Classification Hydrocarbons Alkanes Cycloalkanes Alkenes Cycloalkenes Alkynes 1. Alkanes (saturated) hydrocarbons, or aliphatic hydrocarbons) A. General formula of CnH2n+2 B. Examples a. CH4 b. C2H6 c. C3H? 1. Alkanes (saturated) hydrocarbons, or aliphatic hydrocarbons) A. General formula of CnH2n+2 B. Examples a. CH4 b. C2H6 c. C3H8 d. C4H? 1. Alkanes (saturated) hydrocarbons, or aliphatic hydrocarbons) A. General formula of CnH2n+2 B. Examples a. CH4 b. C2H6 C. Draw Lewis Structures c. C3H8 d. C4H10 1. Alkanes (saturated) hydrocarbons, or aliphatic hydrocarbons) A. General formula of CnH2n+2 B. Examples a. CH4 b. C2H6 C. Draw Lewis Structures H C H H H CH4 c. C3H8 d. C4H10 1. Alkanes (saturated) hydrocarbons, or aliphatic hydrocarbons) A. General formula of CnH2n+2 B. Examples a. CH4 b. C2H6 c. C3H8 C. Draw Lewis Structures H C H H H H CH4 H H C C H H H C2H6 d. C4H10 1. Alkanes (saturated) hydrocarbons, or aliphatic hydrocarbons) A. General formula of CnH2n+2 B. Examples a. CH4 b. C2H6 c. C3H8 d. C4H10 C. Draw Lewis Structures H C H H H H CH4 H H C C H H H C2H6 H H H H C C C H H H H C3H8 1. Alkanes (saturated) hydrocarbons, or aliphatic hydrocarbons) A. General formula of CnH2n+2 B. Examples a. CH4 b. C2H6 c. C3H8 d. C4H10 C. Draw Lewis Structures H C H H H H CH4 H H C C H H H C2H6 D. Polarity? Polar or nonpolar? H H H H C C C H H H H C3H8 1. Alkanes (saturated) hydrocarbons, or aliphatic hydrocarbons) A. General formula of CnH2n+2 B. Examples a. CH4 b. C2H6 c. C3H8 d. C4H10 C. Draw Lewis Structures H C H H H H CH4 H H C C H H H C2H6 H H H H C C C H H H H C3H8 D. Polarity? Polar or nonpolar? Nonpolar E. Types of carbon 1. 2. 3. 4. Primary (1◦) Carbon connected to one carbon atoms. Secondary (2◦) Carbon connected to two carbon atoms. Tertiary (3◦) Carbon connected to three carbon atoms. How many primary, secondary, and tertiary carbons in the two different structures of C4H10 E. Types of carbon 1. 2. 3. 4. Primary (1◦) Carbon connected to one carbon atoms. Secondary (2◦) Carbon connected to two carbon atoms. Tertiary (3◦) Carbon connected to three carbon atoms. How many primary, secondary, and tertiary carbons in the two different structures of C4H10 H H H H H C C C C H H H H H Butane, C 4H10 Primary carbon = ? Secondary carbon = Tertiary carbon = E. Types of carbon 1. 2. 3. 4. Primary (1◦) Carbon connected to one carbon atoms. Secondary (2◦) Carbon connected to two carbon atoms. Tertiary (3◦) Carbon connected to three carbon atoms. How many primary, secondary, and tertiary carbons in the two different structures of C4H10 H H H H H C C C C H H H H H Butane, C 4H10 Primary carbon = 2 Secondary carbon = ? Tertiary carbon = E. Types of carbon 1. 2. 3. 4. Primary (1◦) Carbon connected to one carbon atoms. Secondary (2◦) Carbon connected to two carbon atoms. Tertiary (3◦) Carbon connected to three carbon atoms. How many primary, secondary, and tertiary carbons in the two different structures of C4H10 H H H H H C C C C H H H H H Butane, C 4H10 Primary carbon = 2 Secondary carbon = 2 Tertiary carbon = E. Types of carbon 1. 2. 3. 4. Primary (1◦) Carbon connected to one carbon atoms. Secondary (2◦) Carbon connected to two carbon atoms. Tertiary (3◦) Carbon connected to three carbon atoms. How many primary, secondary, and tertiary carbons in the two different structures of C4H10 H H H H H C C C C H H H H H Butane, C 4H10 Primary carbon = 2 Secondary carbon = 2 Tertiary carbon = ? G. Types of carbon 1. 2. 3. 4. Primary (1◦) Carbon connected to one carbon atoms. Secondary (2◦) Carbon connected to two carbon atoms. Tertiary (3◦) Carbon connected to three carbon atoms. How many primary, secondary, and tertiary carbons in the two different structures of C4H10 H H H H H C C C C H H H H H Butane, C 4H10 Primary carbon = 2 Secondary carbon = 2 Tertiary carbon = 0 E. Types of carbon 1. 2. 3. 4. Primary (1◦) Carbon connected to one carbon atoms. Secondary (2◦) Carbon connected to two carbon atoms. Tertiary (3◦) Carbon connected to three carbon atoms. How many primary, secondary, and tertiary carbons in the two different structures of C4H10 H H C H H H H C C C H H H H Isobutane C4H10 Primary carbon = ? Secondary carbon = Tertiary carbon = G. Types of carbon 1. 2. 3. 4. Primary (1◦) Carbon connected to one carbon atoms. Secondary (2◦) Carbon connected to two carbon atoms. Tertiary (3◦) Carbon connected to three carbon atoms. How many primary, secondary, and tertiary carbons in the two different structures of C4H10 H H C H H H H C C C H H H H Isobutane C4H10 Primary carbon = 3 Secondary carbon = ? Tertiary carbon = E. Types of carbon 1. 2. 3. 4. Primary (1◦) Carbon connected to one carbon atoms. Secondary (2◦) Carbon connected to two carbon atoms. Tertiary (3◦) Carbon connected to three carbon atoms. How many primary, secondary, and tertiary carbons in the two different structures of C4H10 H H C H H H H C C C H H H H Isobutane C4H10 Primary carbon = 3 Secondary carbon = 0 Tertiary carbon = ? G. Types of carbon 1. 2. 3. 4. Primary (1◦) Carbon connected to one carbon atoms. Secondary (2◦) Carbon connected to two carbon atoms. Tertiary (3◦) Carbon connected to three carbon atoms. How many primary, secondary, and tertiary carbons in the two different structures of C4H10 H H C H H H H C C C H H H H Isobutane C4H10 Primary carbon = 3 Secondary carbon = 0 Tertiary carbon = 1 1. Alkanes (Continued) F. There are two different structures for C4H 10 called isomers, because they contain different types of carbon. Structure 1 H H H H H C C C C H H H H H Butane, C 4H10 H Structure 2 H C H H H H C C C H H H H Isobutane, C 4H10 Isomerism Constitutional Isomers (Structural Isomers) are different compounds of the same formula. The different structures from the previous slide for the formula C4H10 is an example of Constitutional isomers. Isomerism Constitutional Isomers (Structural Isomers) are different compounds of the same formula. The different structures from the previous slide for the formula C4H10 is an example of Constitutional isomers. How many isomers are there of an alkane containing five carbons (C5H12)? Isomer Strategy – Draw Lewis possible different length chains of carbons atoms connected with a covalent bond. Isomerism Constitutional Isomers (Structural Isomers) are different compounds of the same formula. The different structures from the previous slide for the formula C4H10 is an example of Constitutional isomers. How many isomers are there of an alkane containing five carbons (C5H12)? Isomer Strategy – Draw Lewis possible different length chains of carbons atoms connected with a covalent bond. Chains of 5 carbon atoms H H H H H H C C C C C H H H H H H Isomerism Chains of 4 carbon atoms H H H H H C C C C H H H C HH H H Isomerism Chains of 4 carbon atoms H H H H H C C C C H H H C HH H Chains of 3 carbon H atoms HH C H H H H C C C HH C HH H H Isomerism Chains of 4 carbon atoms H H H H C C C H H H C H C Chains of 3 carbon atoms H HH C H H H HH H H C C C HH C HH H There are three isomers of C5H12 H NOMENCLATURE 1. Common system a. Works best for low molecular weight hydrocarbons b. Steps to give a hydrocarbon a common name: 1. Count the total number of carbon atoms in the molecule. 2. Use the Latin root from the following slide that corresponds to the number of carbon atoms followed by the suffix “ane”. 3. Unbranced hydrocarbons use the prefix normal, or n-, 4. Branched hydrocarbons use specific prefixes, as shown on a subsequent slide NOMENCLATURE Common system Examples 1. Give a name for the following compound H H H H C C C H H H H Step #1, count the number of carbons and write down the memorized Latin name for that number (next slide) Step #2, since this structure fits the alkane general formula, use the “ane” suffix propane Three carbon Latin root Alkane suffix Latin Hydrocarbon Roots Latin Hydrocarbon Roots Number of Latin Carbons Root Number of Latin Carbons Root Examples H H H H H C C C H C H H H H n-butane H H C H H H 1 meth 12 dodec 2 eth 13 tridec 3 prop 14 tetradec H H H 4 but 15 pentadec isobutane 5 pent 16 hexadec 6 hex 17 heptadec 7 hept 18 octadec 8 oct 19 nonadec 9 non 20 eicos 10 dec 21 unicos 11 undec 22 doicos H C C C H H H H C H H H C C C H H H C H H H neopentane 2. Systematic System of Nomenclature (IUPAC) •Find the longest continuous chain of carbon atoms. •Use a Latin root corresponding to the number of carbons in the longest chain of carbons. •Follow the root with the suffix of “ane” for alkanes •Carbon atoms not included in the chain are named as substituents preceding the root name with Latin root followed by “yl” suffix. •Number the carbons, starting closest to the first branch. •Name the substituent's attached to the chain, using the carbon number as the locator in alphabetical order. •Use di-, tri-, etc., for multiples of same substituent. • If there are two possible chains with the same number of carbons, use the chain with the most substituent's. Substituent Names (Alkyl groups) Systematic Nomenclature continued. H3C CH CH2 CH3 CH3 H3C CH2 C CH CH2 CH2 CH3 CH3 H3C CH CH2 CH3 CH3 H3C CH2 C CH3 CH CH2 CH2 CH3 Which one? Systematic Nomenclature continued. H3C CH CH2 CH3 CH3 H3C CH2 C Which one? CH CH2 CH2 CH3 CH3 H3C The one with the most number of substituent's CH CH2 CH3 CH3 H3C CH2 C CH3 CH CH2 CH2 CH3 Systematic Nomenclature continued. H3C CH CH2 CH3 CH3 H3C CH2 C Which one? CH CH2 CH2 CH3 CH3 H3C The one with the least number of substituent's CH CH2 CH3 CH3 H3C CH2 C CH3 CH CH2 CH2 CH3 The top structure has four substituent's and the bottom has three substituent's. Systematic Nomenclature continued. H3C CH CH2 CH3 CH3 H3C CH2 C Which one? CH CH2 CH2 CH3 CH3 H3C The one with the least number of substituent's CH CH2 CH3 CH3 H3C CH2 C CH3 Name = ? CH CH2 CH2 CH3 The top structure has four substituent's and the bottom has three substituent's. Systematic Nomenclature continued. H3C CH CH2 CH3 CH3 H3C CH2 C Which one? CH CH2 CH2 CH3 CH3 H3C The one with the most number of substituent's CH CH2 CH3 CH3 H3C CH2 C CH CH2 CH3 Name = ? heptane CH2 CH3 The top structure has four substituent's and the bottom has three substituent's. Systematic Nomenclature continued. H3C CH CH2 CH3 CH3 H3C CH2 C Which one? CH CH2 CH2 CH3 CH3 H3C The one with the least number of substituent's CH CH2 CH3 CH3 H3C CH2 C CH CH2 CH2 CH3 CH3 Name = 3,3,5-trimethyl-4-propylheptane The top structure has four substituent's and the bottom has three substituent's. Another Example: CH3 CH3 H3C CH CH CH2 CH2 CH CH3 CH2CH3 Name = 3-ethyl-2,6-dimethylheptane Another Example: CH3 CH3 H3C CH CH CH2 CH2 CH CH3 CH2CH3 Name = 3-ethyl-2,6-dimethylheptane Notice substituent's are in alphabetical order; di, tri, etc. do not participate in the alphabetical order Line Structures A quicker way to write structures' CH3 CH3 H3C CH CH CH2 CH2 CH CH3 CH2CH3 ethyl methyl (A line structure of the above condensed structure) methyl (Condensed Structure) Complex Substituent's •If the branch has a branch, number the carbons from the point of attachment. •Name the branch off the branch using a locator number. •Parentheses are used around the complex branch name. 3 1 1 2 1-methyl-3-(1,2-dimethylpropyl)cyclohexane Alkane Physical Properties Solubility: hydrophobic (not water soluble) Density: less than 1 g/mL (floats on water) Boiling points increase with increasing carbons (little less for branched chains) due to dispersion forces being larger. Melting points increase with increasing carbons (less for odd-number of carbons). Boiling Points of Alkanes Branched alkanes have less surface area contact, so weaker intermolecular forces. Melting Points of Alkanes Branched alkanes pack more efficiently into a crystalline structure, so have higher m.p. Reactions of Alkanes I. Combustion reaction H heat H C H CO2 + H2O + O2 H heat CO2 + H2O + O2 II. Cracking reaction heat + catalyst III. Halogenation reaction (substitution reaction) sun + HCl + + Cl2 Cl Butane 2-chlorobutane Cl 1-chlorobutane Sample problem: Which isomer of C5H12 has the most monochloro isomers? Problem solving process: Step 1 draw the isomers of C5H12 Step 2 react each isomer with chlorine Step 3 count the products Sample problem: Which isomer of C5H12 has the most monochloro isomers? Problem solving process: Step 1 draw the isomers of C5H10 Step 2 react each isomer with chlorine Step 3 count the products + Cl2 + Cl2 + Cl2 Sample problem: Which isomer of C5H12 has the most monochloro isomers? Problem solving process: Step 1 draw the isomers of C5H10 Step 2 react each isomer with chlorine Step 3 count the products Cl + Cl2 + Cl2 + + 2-chloropentane + Cl2 Cl Cl 1-chloropentane 3-chloropentane Sample problem: Which isomer of C5H12 has the most monochloro isomers? Problem solving process: Step 1 draw the isomers of C5H10 Step 2 react each isomer with chlorine Step 3 count the products Cl + Cl2 Cl + + 2-chloropentane Cl 1-chloropentane Cl 3-chloropentane Cl + Cl2 Cl Cl 1-chloro-3-methylbutane 2-chloro-3-methylbutane 2-chloro-2-methylbutane 1-chloro-2-methylbutae + Cl2 Sample problem: Which isomer of C5H12 has the most monochloro isomers? Problem solving process: Step 1 draw the isomers of C5H10 Step 2 react each isomer with chlorine Step 3 count the products Cl Cl + Cl2 + + Cl 1-chloropentane Cl 2-chloropentane 3-chloropentane Cl + Cl2 Cl Cl 1-chloro-3-methylbutane 2-chloro-3-methylbutane 2-chloro-2-methylbutane 1-chloro-2-methylbutae Cl + Cl2 1-chloro-2,2-dimethylpropane Sample problem: Which isomer of C5H12 has the most monochloro isomers? Problem solving process: Step 1 draw the isomers of C5H10 Step 2 react each isomer with chlorine Step 3 count the products Cl Cl + Cl2 + + Cl 1-chloropentane Cl 2-chloropentane 3-chloropentane Cl + Cl2 Cl Cl 1-chloro-3-methylbutane 2-chloro-3-methylbutane 2-chloro-2-methylbutane 1-chloro-2-methylbutae Cl + Cl2 1-chloro-2,2-dimethylpropane Winner! Conformers of Alkanes •Structures resulting from the free rotation of a C-C single bond •May differ in energy. The lowest-energy conformer is most prevalent. •Molecules constantly rotate through all the possible conformations. Ethane Conformers Staggered conformer has lowest energy. Dihedral angle = 60 degrees H H H Dihedral angle H H H Newman projection model sawhorse Ethane Conformers (2) Eclipsed conformer has highest energy Dihedral angle = 0 degrees => Conformational Analysis •Torsional strain: resistance to rotation. •For ethane, only 12.6 kJ/mol => Propane Conformers Note slight increase in torsional strain due to the more bulky methyl group. Butane Conformers C2-C3 Highest energy has methyl groups eclipsed. Steric hindrance Dihedral angle = 0 degrees totally eclipsed (methyl groups) => Butane Conformers (2) Lowest energy has methyl groups anti. Dihedral angle = 180 degrees Staggered-anti => Butane Conformers (3) •Methyl groups eclipsed with hydrogens •Higher energy than staggered conformer •Dihedral angle = 120 degrees Eclipsed (hydrogen and methyl) => Butane Conformers (4) •Gauche, staggered conformer •Methyls closer than in anti conformer •Dihedral angle = 60 degrees Staggered-gauche => Conformational Analysis Cycloalkanes •Rings of carbon atoms (-CH2- groups) •Formula: CnH2n •Nonpolar, insoluble in water •Compact shape •Melting and boiling points similar to branched alkanes with same number of carbons •Slightly unsaturated compared to alkanes Naming Cycloalkanes •Count the number of carbons in the cycle •If the bonds are single then use the suffix “ane” •First substituent in alphabet gets lowest number. •May be cycloalkyl attachment to chain. cyclopropane cyclobutane CH 3 mehtylcyclopropane cyclopentane H3CH 2C cyclohexane cycloheptane CH 3 1-ethyl-2-methylcyclobutane 2-cyclopropylheptane Cis-Trans Isomerism (a type of stereoisomerism) Cis: like groups on same side of ring Trans: like groups on opposite sides of ring Cycloalkane Stability • 6-membered rings most stable • Bond angle closest to 109.5 • Angle (Baeyer) strain • Measured by heats of combustion per -CH2 - Heats of Combustion/CH2 Alkane + O2 CO2 + H2O 697.1 658.6 kJ Long-chain 686.1 664.0 658.6 662.4 663.6 kJ/mol Cyclopropane • Large ring strain due to angle compression • Very reactive, weak bonds => Cyclopropane (2) Torsional strain because of eclipsed hydrogens Cyclobutane • Angle strain due to compression • Torsional strain partially relieved by ring puckering => Cyclopentane • If planar, angles would be 108, but all hydrogens would be eclipsed. • Puckered conformer reduces torsional strain. Cyclohexane • Combustion data shows it’s unstrained. • Angles would be 120, if planar. • The chair conformer has 109.5 bond angles and all hydrogen's are staggered. • No angle strain and no torsional strain. Chair Conformer Boat Conformer Conformational Energy Axial and Equatorial Positions Monosubstituted Cyclohexanes 1,3-Diaxial Interactions Disubstituted Cyclohexanes Cis-Trans Isomers Bonds that are cis, alternate axial-equatorial around the ring. CH3 CH3 One axial, one equatorial => Bulky Groups • Groups like t-butyl cause a large energy difference between the axial and equatoria l conformer. • Most stable conformer puts t-butyl equatorial regardless of other substituents. => End of Chapter 2