Exam 2 Study Guide Lectures 8 15 Lecture 8 September 17 Constitutional isomer same molecular formula but different connectivity Understand what a constitutional isomer is and be able to identify them if given pictures of molecules Naming Alkanes Unbranced alkane ane o Example n pentane n nonane Branched alkane Find longest continuous chain and use the root as its name o Know and be able to recognize and name common substituents Methyl Ethyl Propyl Isopropyl Isobutyl Sec butyl Tert butyl o If there are substituents Name and number each substituent Number the chain so that the substituent has the lowest number possible If there are two or more identical substituents Number the chain so that the substituent that occurs first gets the lowest numberIf there are two or more different substituents CHEM 333 tion 1st Edi List the substituents in alphabetical order Number the chain so that the first substituent encountered gets the lowest number possible o Remember that di tri tetra etc are not included in alpabetizing o When there are many substituents remember to choose the chain that allows it to have the most substituents on it Naming Cycloalkanes Cyclo prefix for number of C ane o Example cyclopentane cyclononane If there is one substituent there is no number o Example methylcyclopentane If there is two substituents list alphabetically If there is three substituents list alphabetically and number with the lowest numbers pos sible o Example 2 ethyl 1 4 dimethylcyclohexane Naming Alkenes Alkynes Be able to name these using similar rules to how to name alkanes Classifying Carbons Primary 1 carbon attached to 1 C Secondary 2 carbon attached to 2 C s Tertiary 3 carbon attached to 3 C s Quarternary 4 carbon attached to 4 C s Lecture 9 September 24 Newman Projections Know how to draw o o The Y shape denotes front C and substituents o The circle denotes back C with 3 lines off of it for substituents o Dihedral angle Angle between C H bond on front C and C H bond on back C o Understand staggered versus eclipsed positions Eclipsed conformation where front H eclipses back H Staggered conformation furthest apart Know how to draw a relative energy diagram along 360 degree rotations for different New man Projections Use knowledge of which conformations are higher in energy over other conformations to fill in the energy diagram that is given Strains of Conformations Know how to identify o Torsional strain from eclipsing interactions o Steric strain when nonbonded atoms separated by four or more bonds are forced closer than atomic radius will allow o Angle strain bond angle is expanded or compressed from its optimal value Gauche two substituents one on front C one on back C with a 60 degree angle Do not look at hydrogens only substituents Gauce interactions are unfavorable higher energy interactions Anti two substituents are 180 degrees apart Lecture 10 September 26 Cyclohexane Conformations Know how to draw chair conformation which has 109 5 degree angle and does not have angle or torsional strain Understand the difference between axial and equitorial positions o If asked to draw the chair conformation and given a compound drawn with wedges and dashes if the element is on a wedge it will always be facing up If the element is on a dash it will always be facing down This will help you determine if it is axial or equitorial depending on where you draw it on the chair Know other conformations of cyclohexane o Know the energies of the other conformations and be able to compare them to one another Know how to draw chair with ring flip o Be able to identify the more stable conformation If there is only one substituent the conformation with it in the equtiorial position is most stable If there are two substituents the conformation with them both in the equitorial position is most stable If both substituents cannot be in the equitorial position and one is equitorial and one is axial the one with the larger substituent in the equitorial position is more stable Know the difference between cis and trans o cis substituents on same side of ring o trans substituents on opposite side of ring cis on left trans on right Lecture 11 October 1 Properties of Alkanes Not polar not miscible with water Good for oxidizing burn fuel Number of carbons affects state of alkane o 1 C to 4 C gas at room temperature cooking fuels o 5 C to 17 C liquid at room temperature gas o 18 C or more wax at room temperature candles The higher the molecular weight the higher the boiling point o Larger molecules higher boiling point more surface area therefore stronger interaction more interaction o Small molecules lower boiling point less surface area therefore weaker inter action less interaction o Constitutional isomers that are branched have lower boiling point and lower melting point less surface area less interaction Synthesis of Alkanes Know how to draw these reactions o Double bond or triple bond is taken away and just becomes a single bond Stereochemistry study of molecules as 3D objects Know how to tell if something is the same compound constitutional isomer enantiomer or diasteromers o Enantiomers chiral molecules that have nonsuperposable mirror images of each other o Diastereomer steroisomers whose molecules are not mirror images of each other o Understand chirality o Chirality the handedness of molecules Look at mirror images of superposable things If superposable not chiral If not superposable chiral Something is not chiral achiral if there is elements of symmetry Lecture 12 October 3 Assigning Priority Rules The higher the atoms number the higher the priority o H C N O S Cl Br I If there is a tie go the the next atom Break the tie at the first point of difference If 2 carbons have the same atom of same priority the one that has more wins Double triple bonds bonded to equivalent number of phantom atoms by single bonds o Examples phantom atoms act like atom is bound to it for priority rules Assigning R or S Locate chiral center and assign priorities Put lowest priority away from you Find directionality of 3 other groups clockwise or counterclockwise Clockwise is R coun terclockwise is S Finding number of stereoisomers If there are two or more chircal centers o n of stereogenic centers o of steroisomers 2n Example n 2 22 4 steroisomers mixtures of enantiomers and diastereomers Example n 3 23 8 steroisomers Lecture 13 October 8 Meso compounds compound that has two or more chiral centers but is not chiral has a plane of symmetry