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CHAPTER 10--ALKANES Dr. Ellen Wilson, RPh, PhD CHE1230 WHY ARE THERE SO MANY ORGANIC COMPOUNDS? WHY ARE THERE SO MANY CARBON COMPOUNDS? Carbon forms stable, covalent bonds with other carbon atoms What does this mean? TYPES OF BONDING Covalent Bonding Ionic Bonding Sharing of electrons Transfer of electrons CH3CH2CH2CH2CH3 Na+ + Cl- = NaCl Organic chemistry bonding Inorganic chemistry bonding Partial charges & dipole moments Full charges, ions Discrete molecules Dissolve but don’t dissociate Nonelectrolytes Lattice structures Dissociate in water Electrolytes WHY ARE THERE SO MANY ORGANIC COMPOUNDS? Carbon forms stable, covalent bonds with other atoms such as H, O, N, S, and halogens WHAT IS A FUNCTIONAL GROUP? A specific group of atoms within a molecule that help define the properties and reactivity of the molecule Will have the same properties regardless of the molecule to which it is attached COMMON FUNCTIONAL GROUPS See inside back cover of text for these examples and more…. FUNCTIONAL GROUPS MAKE A BIG DIFFERENCE Butane Pentane Butanol Gas Liquid Liquid BP=-0.5oC 36.1oC 117.73oC Insoluble in water Soluble FUNCTIONAL GROUPS GIVE UNIQUE PROPERTIES Many biologically active molecules are esters, ethers, carboxylic acids, and amines FUNCTIONAL GROUPS ALLOW US TO PREDICT PROPERTIES OF MOLECULES All alcohols will have the same general properties All amines will have the same general properties All carboxylic acids will have the same general properties Even within a larger molecule, the functional group will have predictable properties even if they are not the properties of the entire molecule WHY ARE THERE SO MANY ORGANIC COMPOUNDS? Carbon can form double and triple bonds with other carbon atoms or other atoms WHY ARE THERE SO MANY ORGANIC COMPOUNDS? The number of ways that carbon and other atoms can combine is almost limitless TWO COMPOUNDS CAN HAVE EXACTLY THE SAME MOLECULAR FORMULAS BUT HAVE DIFFERENT PROPERTIES BASED ON THE ARRANGEMENT OF THE ATOMS Each of the statements given below is true but John Dalton may have had trouble explaining them with his atomic theory. Give explanations for each of the following statements: ethyl alcohol and dimethyl ether have the same composition by mass—52% carbon, 13% hydrogen, and 35% oxygen. However, they have different melting points, boiling points, and solubility in water. COMPOUNDS THAT HAVE THE SAME MOLECULAR FORMULA BUT DIFFERENT STRUCTURAL FORMULAS ARE CALLED STRUCTURAL ISOMERS IN LAB, YOU HAVE ALREADY DISCOVERED SOME OF THE PROPERTIES OF HYDROCARBONS WHAT MAKES THE PHYSICAL PROPERTIES OF HYDROCARBONS DIFFERENT FROM THE PHYSICAL PROPERTIES OF INORGANIC COMPOUNDS? BONDING MAKES THE DIFFERENCE Covalent Bonding Ionic Bonding Sharing of electrons Transfer of electrons CH3CH2CH2CH2CH3 Na+ + Cl- = NaCl Organic chemistry bonding Inorganic chemistry bonding Partial charges & dipole moments Full charges, ions Discrete molecules Dissolve but don’t dissociate Nonelectrolytes Lattice structures Dissociate in water Electrolytes HOW DO MELTING/BOILING POINTS DIFFER? Organic Compounds Low MP and BP Inorganic Compounds High MP and BP HOW DOES SOLUBILITY DIFFER? Organic Compounds Often insoluble in water Why? Why not? Inorganic Compounds Soluble in water Why? HOW DO REACTION RATES DIFFER? Organic Compounds Often slow to react Inorganic Compounds Much easier to react COMPARISON METHANE Type of bonding? BP = -164oC MP = -182oC Slightly soluble in water Flammable Slow to react Can be S, L or G Nonelectrolyte NaCl Type of bonding? BP = 1433oC MP = 801oC 36g/100mL water Nonflammable Quick to react Exists at S at RT Electrolyte OVERVIEW OF HYDROCARBONS Hydrocarbons Alkanes &cycloalkanes aliphatic aromatic alkenes alkynes WHAT ARE ALKANES? Saturated Base molecule contains only C and H No double or triple bonds THE FIRST FOUR ALKANES Methane, CH4, ethane, propane, butane C2H6, C3H8, C4H10 A MOLECULAR FORMULA CH4, C2H6, C3H8, C4H10 GIVES THE TYPE AND NUMBER OF ATOMS IN THE COMPOUND BUT TELLS NOTHING ABOUT THE STRUCTURE OF THE COMPOUND A STRUCTURAL FORMULA GIVES THE ACTUAL ARRANGEMENT OF THE ATOMS IN A MOLECULE H H H H H H H H H H A CONDENSED FORMULA REPRESENTS THE ARRANGEMENT OF THE ATOMS WITHOUT DRAWING ALL THE BONDS CH4 CH3CH3 CH3CH2CH3 CH3CH2CH2CH3 STRUCTURAL AND CONDENSED FORMULAS ARE ESPECIALLY USEFUL WHEN DEALING WITH STRUCTURAL ISOMERS butane isobutane C4H10 C4H10 CH3CH2CH2CH3 (CH3)3CH H H H H H H H H H H H H H H H H H H H H REMEMBER, REMEMBER, REMEMBER…… CARBON FORMS 4 BONDS HYDROGEN FORMS 1 BOND STRUCTURAL AND CONDENSED FORMULAS ARE ESPECIALLY USEFUL WHEN DEALING WITH ISOMERS pentane isopentane C5H12 C5H12 CH3CH2CH2CH2CH3 CH3CH(CH3)CH2CH3 H H H H H H H H H H H H H H H H H H H H H H H H PRACTICE: Write the structural formulas from the following condensed formulas: CH3CH2C(CH3)3 (CH3)3CC(CH3)3 (CH3)3CBr PRACTICE: H H H H H H H H H H H H H Write the condensed formulas from the following structural formulas: H H H H H H HH H H H H H H H H H H H H H H H H H H H H H H H H Br H H NOMENCLATURE OF ALKANES NAME the parent compound The first TEN straight chain alkanes are: Methane Ethane Propane Butane Pentane Hexane Heptane Octane Nonane Decane NOMENCLATURE OF ALAKNES NUMBER the parent compound Find the longest chain Start numbering so that any substituents get the lowest number possible REPRESENTATIVE SUBSTITUENTS --CH3 --CH2CH3 --CH2CH2CH3 --CH2CH2CH2CH3 --CH2CH2CH2CH2CH3 --F --Br --Cl --I EXAMPLES: Name & number the longest continuous carbon chain Name and number the substituent H H H H H H H Br EXAMPLES: Name & number the longest continuous carbon chain Name and number the substituent Cl H H H H H H H H H EXAMPLES: Name & number the longest continuous carbon chain Name and number the substituent I H H H H H H H H H H H H I MORE EXAMPLES: Name & number the longest continuous carbon chain Name and number the substituent H H H H H H H H H H H H H H H H H H H H H H H H H H H H MORE EXAMPLES: Name & number the longest continuous carbon chain Name and number the substituent H H H H H H H H H H H H H HH H H H REACTIONS OF ALKANES Combustion An alkane + oxygen gives carbon dioxide plus water An important side reaction? REACTIONS OF ALKANES Halogenation—an alkane plus a halogen gives an alkyl halide (substituted alkane) plus a hydrogen halide (acid) CH4 + Br2 → CH3-Br + HBr CH3CH3 + Cl2 → CH3CH2-Cl + HCl IS YOUR CYCLOALKANE A BOAT OR A CHAIR? IS YOUR HYDROGEN AXIAL OR EQUATORIAL?