hem 20 Lewis Structures 1. Draw complete Lewis structures, showing all atoms and lone pairs, for the following molecules. 4 3 Br Br 3 3 2 3 2 2 4 + 3 + 2 2 2 4
P 3 3 3 3 3 Formal harge 1. Given the following Lewis structures, identify the formal charge on all the non-hydrogen atoms. You may assume that all atoms and lone pairs are shown completely and correctly. (anything not marked has a formal charge of zero) hem 20
hem 20 rbitals and ybridization 1. Each of the following species contains a carbon-nitrogen bond. Give the hybridization of both the carbon and nitrogen atoms, describe how each of the orbitals is used (for -bonding, -bonding, lone pairs, etc.), and how these orbitals form the carbon-nitrogen bond. *: sp 3 ;uses4sp 3 orbitals to make 4 sigma bonds *: sp 3 ;uses3sp 3 orbitals to make 3 sigma bonds, and 1 to hold lone pair *- single bond formed from end-to-end overlap of sp 3 and sp 3 to form a sigma bond + *: sp 3 ;uses4sp 3 orbitals to make 4 sigma bonds *: sp 3 ;uses4sp 3 orbitals to make 4 sigma bonds *- single bond formed from end-to-end overlap of sp 3 and sp 3 to form a sigma bond *: sp 2 ; uses 3 sp 2 orbitals to make 3 sigma bonds, with remaining 2p orbital contributing to pi bond *: sp 2 ;uses2sp 2 orbitals to make 2 sigma bonds and 1 to hold lone pair, with remaining 2p orbital contributing to pi bond *- double bond formed from end-to-end overlap of sp 2 and sp 2 to form asigmabond,andside-by-sideoverlapof 2p and 2p to make a pi bond *: sp; uses 2 sp orbitals to make 2 sigma bonds, with remaining 2p orbitals contributing to two pi bonds *: sp; uses 1 sp orbital to make a sigma bond and 1 to hold lone pair, with remaining 2p orbitals contributing to two pi bonds *- triple bond formed from end-to-end overlap of sp and sp to form asigmabond,andside-by-sideoverlapof both2p and 2p orbitals to make two pi bonds 3
"Skeletal" Structures 1. For each of the following skeletal structures, draw a complete Lewis structure showing all atoms, lone pairs, and formal charges. (Each structure has any formal charges already indicated.) hem 20
hem 20 Electronic and Molecular Geometry 1. omplete the following Lewis structures by drawing in lone pairs. Then, identify the electron-pair geometry and molecular geometry of each of the non-hydrogen atoms. EPG = electron-pair geometry MG = molecular geometry EPG: tetrahedral MG: tetrahedral EPG: tetrahedral MG: bent EPG: trigonal planar EPG: trigonal planar MG: trigonal planar EPG: trigonal planar MG: trigonal planar EPG: trigonal planar MG: trigonal planar EPG: tetrahedral MG: tetrahedral EPG: linear MG: linear EPG: trigonal planar EPG: tetrahedral MG: tetrahedral EPG: trigonal planar MG: trigonal planar EPG: linear MG: linear 4
hem 20 Resonance 1. For each of the following, complete the Lewis structure by drawing in all the implied lone pairs. Then draw the single best alternate resonance structure. Then indicate which of the two structures is more stable, or if they are equally stable. 2 2 2 2 equally stable 3 equally stable 3 more stable 3 2 3 2 3 3 3 3 3 3 more stable equally stable 3 3 3 3 more stable 3 3
hem 20 urved Arrows 1: Resonance 1. Each of the following molecules exhibits several alternate resonance structures. Show some of these resonance structures, and use curved arrows to keep track of where the electrons are going. most stable alternate res. structure 2 nd most stable alternate res. structure ther possibilities include:
hem 20 "Skeletal" Structures and Resonance 1. For each of the following species, provide a complete Lewis structure, showingall atoms, bonds, and lone pairs. Draw the best alternate resonance structure in the other box. Include all nonzero formal charges. omplete Lewis Structure: Best Alternate Resonance Structure: (connected in that order)
hem 20 ybridization and Resonance When a molecule exhibits resonance, the hybridization and geometry must accomodate the resonance structures. ften this is accomplished by placing a lone pair in a p-orbital rather than in a usual hybrid orbital. 1. Each of the following structures has a lone pair which must go into a p-orbital in order to achieve resonance. Identify each such lone pair, and show the resonance which requires such "re-hybridization." In addition, give the (correct!) hybridization of each non-hydrogen atom. sp 2 This "lone pair" is in a p-orbital - part of a delocalized -system! And this "lone pair" is also in a p-orbital - part of a delocalized - system! sp 2 3 3 3 sp 3 (for both 3 groups) issp 2 hybridized in both resonance structures. 3 And this "lone pair" is also in a p-orbital! sp 2 This "lone pair" is in a p-orbital! sp 3 sp 2 3 3 issp 2 hybridized in both resonance structures. And this "lone pair" is also in a p-orbital! sp sp This "lone pair" is in a p-orbital! sp 3 3 issp 2 hybridized in both resonance structures. 3
hem 20 Arrows and Resonance 1. Each of the following structures has a significant alternate resonance structure. Draw the best alternate resonance structure, and show, using the curved-arrow formalism, how to arrive at the new structure you have drawn starting from the given structure. You may need to add lone pairs to the structure. Then, identify the new resonance structure as less stable, equally stable, or more stable than the given structure. (ote: There may be more that one possible resonance structure which you could draw. Please draw only the best one.) circle: less stable equally stable more stable circle: less stable equally stable more stable circle: less stable equally stable more stable circle: less stable equally stable more stable
hem 20 Alkane omenclature 1. Each of the following "names" does, indeed, describe an alkane. owever, the names are not the correct systematic names for the indicated alkane. Draw the structure described by each name, and give the correct name. an you explain why the given names are not correct? 1-methyl-3-ethylpropane hexane 2-isopropyl-3-methylpentane 2,3,4-trimethylhexane 2,2,3-trimethyl-4-ethylhexane 4-ethyl-2,2,3-trimethylhexane (Same numbering, but substituents in alphabetical order!) 2-methyl-5-tert-butylpentane 2,2,6-trimethylheptane
hem 20 onsider the following molecule: onformational Analysis 1. This molecule has 3 staggered and 3 eclipsed conformations based on rotation around the central - bond. Use the space below to draw all 6 conformations in an unambiguous notation. This is the worst! - eclipsed! 0 o =4.8kcal/mol 2-gauche 60 o =1.8kcal/mol This is the worst! - eclipsed! 120 o =4.8kcal/mol Most stable! 1-gauche 180 o =0.9kcal/mol 3-eclipsed 240 o =3.9kcal/mol Most stable! 1-gauche 180 o =0.9kcal/mol 3. Given the following information, graph the conformational energy of this molecule as a function of rotation around the central bond. ote: Your answer may be shifted from this one, based on which confirmation you chose as 0 degrees and which direction you rotated. For each: 5 eclipsed 1.0 kcal/mol 4 eclipsed 1.3 eclipsed 2.5 3 gauche 0.9 E 2 1 0 0 60 120 180 240 300 360 angle
hem 20 More onformational Analysis 1. onsider the conformations of the following molecule obtained by rotation around the indicated bond: 3 2 3 3 3 a) In terms of rotation around the indicated bond, this molecule should have a single lowest energy conformation. Using a ewman projection, show the lowest-energy conformation of this molecule. Be sure to view the molecule along the indicated bond. 3 2 3 3 3 or 3 3 3 2 3 b) In terms of rotation around the indicated bond, this molecule should have a single highest energy conformation. Using a ewman projection, show the highest-energy conformation of this molecule. Be sure to view the molecule along the indicated bond. or 3 3 3 2 3 3 3 3 2 3 c) Use ewman projections to draw two distinct conformations that would have energy intermediate between the conformations you drew in (a) and (b) above. There are several acceptable answers, including: 3 3 2 3 3 3 3 2 3 3
hem 20 Functional Groups 1. For each of the following molecules, identify and name all the functional groups. ketone alkyne alkene 2 amine (primary) epoxide aromatic ring (arene) Br alkyl halide alcohol amide ether aldehyde ether carboxylic acid alkene nitrile acetal S thiol 2. For each of the following functional groups, provide a simple molecule as an example. acetal alcohol aldehyde alkane alkene alkyne alkyl halide amide amine aromatic ring (arene) carboxylic acid Br 2 epoxide ester ether ketone nitrile thiol S
hem 20 Functional Groups ircle and name all of the functional groups in the following compounds. You may ignore alkanes and aromatic rings. (a) Taxol (an inhibitor of cell division used in cancer chemotherapy, first isolated from the Pacific yew tree) ester ketone amide Ph ester alkene alcohol Ph alcohol alcohol ester ester ether Ph (b) ephalosporin (an antibiotic that disrupts synthesis of the bacterial cell wall) carboxylic acid 2 amide sulfide (or thioether) S alkene amine amide ester carboxylic acid (c) Glutathione (a tripeptide that protects cells from oxidative damage) thiol amide S carboxylic acid 2 amine amide carboxylic acid
hem 20 Functional Groups and ybridization 1. For each of the following molecules, circle and identify all the functional groups in the molecule. Then write the hybridization of each of the indicated atoms in the boxes provided. sp 3 acetal sp 2 sp 3 S thiol alkene sp alkyne amide sp 2 carboxylic acid sp 2 nitrile sp sp 3 ether aldehyde sp 2