CHEM 2211 Exam 1 Study Guide Lectures 9 19 Lecture 9 6 September I II III IV V VI Single bonds rotate about themselves giving rise to geometric isomers a Cis isomers have substituent on the same side b Trans isomers have substituents on opposite sides c Each molecule has a different form of reactivity Conformations are different spatial arrangements while configurations are different compounds Chiral molecules are molecules that are non superimposable mirror images of themselves similar to left and right hand a The result of carbon bonded to four different substituents b Achiral molecules are superimposable mirror images of each other Enantiomers are molecules that cannot be superimposed on each other but are mirror images of each other a When drawing enantiomers remember that the hatched wedge means the bond is receding into the paper and that the wedge means the bond is sticking out at you Fisher projections show that bonds intersect at a vertical carbon a Vertical lines are bonds extending backwards and horizontal lines are bonds extending forwards R S naming system determines the direction of the chiral center a Rank the substituents in order of highest to lowest priority based on their atomic weight i e O N b If lowest priority group is on hatched wedge then draw an arrow from highest priority to lowest It s an R configuration if the arrow is clockwise and S configuration if the arrow is counterclockwise c If lowest priority is not on the hatched wedge then the switch it with the highest priority one and follow the steps presented above Lecture 10 9 September I Though enantiomers have similar properties they interact differently with plane polarized light A Achiral molecules do NOT rotate light B Dextrorotary molecules rotate light to the right C Levorotary molecules rotate light to the left D The specific rotation of a molecule is the measure of the amount of rotation caused by pure liquid or 1 00g of material dissolved in 100 mL E This equation is used to determine the amount of rotation light has done T II lxc F A racemic mixture is the mixture of equal parts of both enantiomers These mixtures yield a rotation of zero Enantiomeric Excess tells us how pure a mixture is via this equation enatiomeric excess observed specific rotation x 100 specific rotationof the pure enantiomer Example 2 bromobutane has a specific rotation of 23 1 An experiment yielded that a 2 bromobutane mixture has an observed specific rotation of 9 2 enatiomeric excess 9 2 x 100 40 23 1 This means that 40 of the mixture is excess S enantiomers and 60 is a racemic mixture meaning a total of 70 40 30 is S enantiomer and the remaining 30 is R enantiomer III A Observed specific rotation is the rotation of the same B Enantiomerically pure compounds only have one enantiomer Compounds with more than one asymmetric center can be diastereomers in which they are neither identical nor mirror images A Diastereomers have different physical and chemical properties B Erythro enantiomers have hydrogens on the same side C Threo enantiomers have hydrogens on the opposite side Lecture 11 11 September I II III Some cyclic compounds have stereoisomers but some do not because they have substituents placed an equal distance from each other Meso compounds are asymmetric centers with a line of symmetry running through the molecule They are achiral and also optically inactive Name molecules with multiple asymmetric centers the same as with one asymmetric center but remember to specify which carbon has the asymmetric center Lecture 12 13 September I HNMR is the measure of the number of molecules aligned with and against a magnetic field a Shielding affects the signal graphed i Shielding refers to the number of electrons around the molecule If an atom is around another very electronegative atom then the atom with be less shielded ii More shielded molecules are upfield right and less shielded are downfiled left b Chemically equivalent hydrogens produce the same signal c Chemical shift is the measure of how far the signaled is from the reference compound TMS Lecture 13 16 September I II The area under the HNMR spikes is equivalent to the number of hydrogens in the compound Signal splitting occurs when nonequivalent hydrogens on adjacent carbons emit a signal that interferes with other hydrogens a N 1 rule is the number of hydrogens on nonequivalent neighboring carbons 1 number of peaks on graph b Hydrogens on prochiral centers are equivalent c Hydrogens on chiral centers are not Lecture 14 18 September I II III IV OH shows up very broad on NMR graphs if it shows a signal Deuterium is used to determine the signal of a molecule because it doesn t show up on HNMR CNMR records the signals of Carbon 13 and requires an FT NMR because the CNMR graph is an average of multiple scans Shows up as singlets in decoupled CNMR but shows as splitting on proton coupled CNMR Lecture 15 20 September I II Alkenes have unsaturated carbons because they have a double bond A Degree of unsaturation is dependent upon number of pi bonds Nomenclature is the same for alkanes but the parent ending is ene III A Number the parent chain in an order that gives the functional group the lowest number double bond counts as a functional group i Use EZ nomenclature as opposed to cis trans B For molecules with two double bonds replace ene with diene C Substituents are stated before the parent chain name The functional group on the parent chain always gets the lowest number D Multiple substituents are stated in alphabetical order for further review refer to Section 3 2 in the book E If same number is found for two substituents when numbered both ways then the way with the lowest substituent number wins F Double bonds in a ring are always labeled as carbons one and two then count to give the substituents the lowest number G If the same number is found for alkene functional groups and for one or more substituents ignore the conflicting substituents and number in a way that gives the remaining substituent the lowest number i Sp2 carbons are called vinyl carbons and their adjacent carbons are called allylic carbons Using the E and Z method A E Z nomenclature refers to the orientation of the highest priority substituents when the substituents are not the same B E means that the substituents are on the same side C Z means the substituents are on the opposite side D Priority is based on the atomic number Lecture 16 19 23 September Summary of Alkene Reaction Mechanisms I II