CHEM 227 1st Edition Lecture 4 Outline of Last Lecture I. 2.7 Acids and Bases: The Bronsted-Lowry DefinitionII. 2.8 Acid and Base strengthIII. 2.9 Predicting Acid-Base Reactions from pKa valuesIV. 2.10 Organic Acids and Organic basesV. 2.11 Acids and Bases: The Lewis DefinitionVI. 2.12 Noncovalent interactions between moleculesOutline of Current Lecture I. 3.1 Functional GroupsII. 3.2 Alkanes and Alkane IsomersIII. 3.3 Alkyl GroupsIV. 3.4 Naming AlkanesV. 3.5 Properties of AlkanesVI. 3.6 Conformations of EthaneVII. 3.7 Conformations of other AlkanesCurrent LectureChapter 33.1 Functional Groups- Functional Group: Collection of atoms at a site that have a characteristic bonding pattern and chemical behavior in all molecules where it occurs.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.3.2 Alkanes and Alkane Isomers- Alkanes: Compounds with C-C single bonds only (no functional groups)- Connecting carbons can lead to large or small molecules- The formula for an alkane with no rings in it is CnH2n+2 where the number of C’s is n- Alkanes = Saturated Hydrocarbonso Have only C-H and C-C single bonds, meaning there is the max number of hydrogens for the number of carbons- Constitutional Isomers: have same molecular formula but are different in connectivity3.3 Alkyl Groups- Alkyl group – (a part of a structure)o Not stable compounds themselves, but parts of larger compounds- General abbreviation “R”- Name: replace -ane ending of alkane with –yl ending- -CH3 is “methyl” (from methane)- -CH2CH3 is “ethyl” from ethane- Can have just straight chain alkyl groups or other varieties of alkyl groups because of different connectivity- Determining Primary vs. Secondary vs. Tertiary vs. Quaternary carbono This can have an effect on reactivity of functional groups/the molecule - Primary vs. Secondary vs. Tertiary vs. Quaternary Hydrogenso Primary hydrogens are attached to primary carbons, secondary hydrogens to secondary carbons, etc.3.4 Naming AlkanesSteps for naming- First find parent hydrocarbon chain (or the longest chain of carbon)- If two different chains are of the same length, choose the one with the greater number of substituents branching off as the parent chain- Number atoms in longest chain starting from the end closest to the first branch point- Identify and number the substituentso Assign a locant to each substituent to locate its point of attachment to the parentchain- Write the name as a single wordo Use hyphens to separate the different prefixes and use commas to separate numbers. If two or more different substituents are present, cite them in alphabetical order, not numberical order. o If two or more identical substituents are present on the parent chain, use one of the multiplier prefixes di-, tri-, tetra-, etc.- Name a complex substituent as though it were itself a compound3.5 Properties of Alkanes- Generally unreactive compared to other functional groupso They will burn in a flame, producing carbon dioxide, water, and heato They react with Cl2 in the presence of light to replace H’s with Cl’s- Boiling points and melting points increase as size of alkane increases- Dispersion forces increase as molecule size increases, resulting in higher melting and boiling points3.6 Conformations of Ethane- Stereochemistry: branch of chemistry concerned with the 3D aspects of molecules- σ bonds are cylindrically symmetrical - free rotation in open-chain molecules- conformations: the different arrangements of atoms that result from bond rotation- Newman projection: a way of looking at a bond between two carbons that shows the directly end-on view and represents the two carbon atoms as a circle, so you can see thebonds on both- There is not perfectly free rotation- An energy barrier to rotation makes some conformers more stable than others- Staggered- most stable: all 6 C-H bonds are as far away as possible- Eclipsed- least stable: all 6 C-H bonds are as close as possible to each other- The farther apart the substituents are, the more stable the bond is- Staggered (60º, 180º, and 300º) are most favored conformations- Torsional strain: the strain caused by the interactions between substituents… the fartheraway the substituents/the smaller the substituents, the less torsional strain3.7 Conformations of other Alkanes- The eclipsed conformer of propane has 3 interactions: two ethane-type H-H interactions,and one H-CH3 interaction- Conformational analysis is more complex for larger alkanes - Not all staggered conformations have same energy, and not all eclipsed conformations have same energy- Conformations of butane- Anti conformation- methyl groups are 180˚ apart- Gauche conformation- methyl groups are 60˚ apart- Steric strain: the repulsive interaction that occurs when atoms are forced closer togetherthan their atomic radii