Study Guide Midterm 2
Study Guide Midterm 2 CEM 251
Popular in Organic Chemistry I
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This 12 page Study Guide was uploaded by Sarah Struble on Friday October 23, 2015. The Study Guide belongs to CEM 251 at Michigan State University taught by C. Vasileiou in Fall 2015. Since its upload, it has received 277 views. For similar materials see Organic Chemistry I in Chemistry at Michigan State University.
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Date Created: 10/23/15
fof12 CEM 251 Midterm 2 Study Guide Chapter 5 Isomers Stereochemistry 3D structure of any molecule Isomers same molecular formula combination is different Isomers Constitutional Isomers Stereoisomers way the atoms are connected is different different 3D orientation in space structural isomers functional group conformational ring flip configuration cistrans isomers f W M chirality isomers M or H M Stereochemistry 3D Structure Chirality group pointing up or down asymmetry asymmetric carbons chiro hand mirror images but cannot be super imposed Chiral Carbon C chiral center can only be sp3 carbons Any time you have a carbon with 4 DIFFERENT groups on it it is a chiral carbon HvC M b H gt 4 of the same groups around C so it is NOT CHIRAL 20f12 Once you find the chiral C number the groups around the carbon Numbering Rules Priority is based on atomic number highest atomic number first priority only number atoms directly bonded to the chiral C see which way the priority numbers increase clockwise or counterclockwise Two Types of Chirality R or S CWCCW 4 Priority Atom dashwedge Chirality CW back dash R CW front wedge S CCW back dash S CCW front wedge R Gila CCW W Cw 2ch W l 399th Wm CJL K b 3 Klosj Cw iash 33 El 23916 9 K s The less H s a carbon has the higher the priority 30f12 How many chiral centers NH 3 HO uC H quot H Chiral Molecules 1 C gt chiral molecule 2 or more C gt it depends if there is NO plane of symmetry gt chiral molecule if there is a plane of symmetry gt achiral meso lbquot 2quot Br if Vlth at m I Enantiomers two chiral molecules whose stereocenters are all opposite example 28 38 vs 2R 3R 1 Ms 0quot 3 CL 3 Ir 7 391 F d Ibr T W15 F 36 m3 4of12 Identical molecules two molecules with all the same stereo centers Diastereomers some stereocenters are different but not all To find the number of stereoisomers a molecule has n number of C 2n number of stereoisomers Fisher Projectons vertical line dashed horizontal line wedge Am gt324 gt all of the atoms in the center have changed sides so these molecules are enantiomers cooH CH 10 H0 k Ho k lt 39ou H0 s k 0it H0 k xi39r on s OH CH pH COOH gt same molecule just rotated 50f12 Ch 6 Chemical Reactivity Types of Organic Reactions 1 Addition Reactions Add groupselements to a starting material SM product has more groups than initial usually the starting material contains pibonds l Or X 2 Eliminations elements of the SMS are eliminated pi bonds formed 3 Substitution Reaction atomgroup on the SMS is replaced by something else losing atom but not losing bond EEZ Y gtampquot Y Z 4 Rearrangement Reaction Single SM that undergoes reorganization of atomsgroupsbonds product will be an isomer 0 210 9 HM OH 6of12 Reaction Mechanism description of how bonds breakform as the SM becomes product 1 Concerted Mechanism no intermediate bonds break and form at same time A d svx 94x 2 Stepwise Mechanism more than one step Ae aCHD ab SM in rm POM Bond Cleavage Mechanisms 1 Homolytic Cleavage radicals a A b one e to one atom one to the other l QIEXQ a H39 2 Heterolytic Cleavage both e go to most electronegative atoms A AC9 H59 53 3 Cutiat union Polar Reactions less electronegative atom l CB Zquot v r C iet Z i U L carbanion 7of12 more electronegative atom l 4 l CB 23 v YGQ I 9 I J C X r carbocation Carbocation Stability the more Rgroups around a carbocation the more stable i ii i i lav Cg C RC RC 9 la L k methyl primary 1 secondary 2 tertiary 3 least stable most stable the e clouds in the R groups are bigger so they stabilize the positive charge on the carbon better Carbanion Stability opposite of carbocation the less Rgroups around a carbocation the more stable the large electron clouds destabilize the negative charge Radical Carbon Stability act like carbocations the more Rgroups around a carbocation the more stable the uncoupled e wants to have an electron next to it the bigger electron clouds from the Rgroups make it more stable 39 39 least stable most stable Polar Reactions Negative always attacks positive Nucleophile negative Electrophile positive so nucleophiles always attack electrophiles Age59 Nw9E39 a W E 80f12 Nucleophiles electron rich species neg charge give electrons ex lone pair negative charge double bond 00 quote A K 2R R 9 r E Electrophiles electron poor species pos charge take e ex positively charged partial pos charge Thermodynamics Products favored gt delta G lt O delta H lt O exothermic releases energy Starting material favored gt Delta G gt O delta H gt O endothermic requires energy Reaction Energy Diagram Concerted Reaction one step NvCQ ece VA QC AC5 assume products are favored l TSft Ea Activation Energy TS Transition State 90f12 Rate is determined by Activation Energy high Ea slower rate of reaction low Ea faster rate of reaction Energy Diagram Stepwise Reaction 2 or more steps Sax fe Aylgag AC 69 Assume first step is faster than second step l a l I 7 I no r no in Step One Step Two if gtwhole reaction exothermic E Ea2 determines the rate since it is higher takes E W more time A B Step 2 Rate determining step Kn Ch 7 Alkyl Halides sp3 Carbon Halogen bond polar bond R R 100f12 i CHme kcfo R i lt Hi X methyl Halide primary 1 secondary 2 tertiary 3 Not AlkylHalide 3 bc of sp2 carbon X allyl vinyl group in if X Vinyl Halide X Benzyl Halide phenyl group Phenyl Halide benzyl group Examples 5V Naming Halo Alkanes vs Alkyl Halides I Dr 1bromo ethane or ethyl bromide 1iodo propane or isopropyl iodide A L Vinyl Chloride 11 Of 12 More on Substitution Reactions I N LC strong nucleophile N LLE weak nucleophile Rxn 1 strong Nuc Ap wA eNeHA 0 69 o 0 w Rxn 2 weak Nuc N r aN SEQ Deprotonation step i VOV H r Rxn 1 and 2 get to the same organic product first step is substitution for BOTH second step in rxn 2 is deprotonation 39 deprotonation usually happens when a weaker nucleophile is used Nufc39 OneStep Reaction No intermediate CH3C NaOH gt CH3OH NaCI rate kCH3CI x NaOH second order because the rate depends on 2 things second order 1 step rxn substitution rxn N Knucleophilic 120f12 8N2 Reactions Transition State one group leaves from one side the other group comes from the other side A 3r SN 39 i attack has to come The CH3 and H move from this side since over to make room the Br is leaving from for the OH the other side Chirality also changes the chirality of products will be opposite of the SM H CH 2 393 mstg r we woC i Rate of 8N2 Rxns the less R groups the faster the reaction methyl halide fastest works with a strong or weak Nuc secondary slowest works with only a strong Nuc or a polar aprotic solvent tertiary halide so slow it doesn t work Will not work with strong or weak Nuc ExamStyle Example 1 Write the major organic product in box 1413 r O lt l l gt l 2 Write the reaction mechanism inf 0H JV N a AM W l K Era
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