CHM 251 Organic Chemistry 1

Transcription

1 CM 251 rganic Chemistry 1 NAME Fall 2008 omework #1 Due: Friday, September 26, :00 pm Print out this assignment and complete all of your work on these pages. Use the back if necessary. 1. Given the following molecules, complete the table shown below. RS C 3 U R A 3 CSSS B D W C 3 R 3 C C 3 N N 3 C X C 2 T C V C 3 F Me Calicheamicin Y Shikimic Acid E Label Functional group Label ybridization state of circled atom A T B C D E F U V W X Y Formal charge on the oxygen in circle C if it uses its lone electron pair to be protonated by an Bronsted-Lowry acid Molecular formula for Shikimic Acid Total number of σ bonds in Shikimic Acid

2 2. Agrochemicals R Us, a new biotech company dedicated to developing plant hormones as potential pesticides has recently marketed the structure shown below. owever, the research and development team has not been able to determine the structure of the active conformation. They turn to you for an answer to this question because of your expertise in conformational analysis. You believe that the active conformation is the one with the lowest potential energy because many biologically-active compounds adopt the structure of the energy minimum when functional. In order to illustrate this idea to management, you will need to generate a graph of potential energy vs. dihedral angle for each 60º rotation about the carbon-carbon bond shown in RED (see the structure) for a total of 360º. Be sure to label the energy differences (as determined from the chart of values, below) on your graph and draw the Newman projections corresponding to each 60º rotation. Also, label each interaction in your Newman projection as eclipsed, gauche, or anti and list whether the strain induced by the structure is torsional, steric, or a combination of the two. defined as the "large group" in the table of values Me Et C 3 Br C 3 Conformational Interaction Δ (kcal/mol) Eclipsing ( and C 3 ) 1.9 Eclipsing ( and C 3 ) 1.6 Eclipsing ( and C 2 C 3 ) 2.1 Eclipsing (C 3 and Br) 2.8 Eclipsing ( and Br) 3.0 Eclipsing (C 2 C 3 and Br) 3.3 Eclipsing (C 3 and large group ) 4.3 Eclipsing (C 2 C 3 and large group ) 4.9 Eclipsing (C 3 and large group ) 4.6 Gauche (C 3 and Br) 1.1 Gauche (C 3 and Br) 0.9 Gauche (Br and C 2 C 3 ) 1.7 Gauche (C 3 and large group ) 2.1 Gauche (C 3 and large group ) 1.9 Gauche (C 2 C 3 and large group ) 2.5

3 3. Name the structure in question #2. 4. During your first day on the job at NazChem Suppliers, your boss has you doing the inventory of the chemical stockroom. Curiously, you come across a series of bottles in which only the molecular formula appears on the label along with some seemingly trivial information. Listed below are some of the formulae and information. Your job is to decipher the formulae by coming up with reasonable Lewis structures for them that are consistent with the extra information. Be sure to perform both degree of unsaturation calculations as well as formal charge calculations in order to verify whether the structures are reasonable or not. (a) C C NMR analysis shows a carbocycle with five methine, one methylene and four methyl groups and a total of four different carbons. (b) C 6 13 N 2 13 C NMR analysis shows an acyclic compound with two methylene, two methyl, and two quaternary carbon groups with a total of five different carbons. (c) C C NMR analysis shows a cyclic structure with only secondary and quaternary carbons and a total of three different carbons. (d) C 7 16 N + -- this acyclic structure must contain a tert-butyl group and a tertiary amine (by the way you found this bottle in the 80 C freezer why?)

4 5. For your Lewis structure from question #4b: (a) Name the compound (b) label the hybridization state for each CARBN atom in the structure (c) for each bond to CARBN in the structure, create a table to list the type of bonds formed (sigma or pi) as well as the orbitals from which the bond was formed (s, p, sp, sp2, sp3, ) you may want to attach an EXCEL table! (d) select any one bond and show the molecular orbital diagram and estimate the amount of energy released upon formation of that bond (e) determine in which type of orbitals any lone electron pairs reside 6. For the structure from question (#4d), describe the hybridization state of the atom carrying the charge, explain your rationale for the assignment and draw an orbital picture to show the structure around the central atom. Be sure to describe the precise location of the positive charge within this molecule can be delocalized or dispersed. There is more than one way to do this, so be complete in your explanation. Draw a series of structures to support your response.

5 7. Not all compounds were created equal in terms of stability. So, with this idea in mind, use resonance to explain the following rank ordering of stability for the four compounds shown below. It is imperative that you draw all possible resonance structures and to weight their relative importance (stability) that is, you need to consider if some resonance structures are better (re; more stable) than others. ne important restriction on this problem: You may move only 2 electrons (either pi or lone pairs) at a time Rank ordering: Least stable Most stable Compounds of interest: #1 #2 #3 #4 Cl 2 N

6 8. Name each of the following structures. 3 C C 3 Br Cl N 2 N 2 Br Cl 3 C C(C 3 )C 2 C 3 N N 2 F C 2 C 3 Cl

7 9. Draw the structures that correspond to the following names. If the compound is named incorrectly, correct it! a. 2,2,4,4-tetramethyl-3-n-butylpentane b. (Z)-4-bromo-3-pentene c. 5-methyl-4-oxohexanoic acid d. N,N-diethyl-2-butanamine (or N,N-diethyl-2-aminobutane) e. 3-ethyl-1-hexen-4-yne f. 2,2,4,6-tetramethylcyclohexanone g. 2-methyl-4-aminocyclohexanecarboxaldehyde h. 3-cyclopropylbutanoyl chloride i. 1,2-dimethyl-5-isopropyl-1-cyclopentene