Biochemistry_Homework_1 - Name Student ID Instructor Yunus...

This preview shows page 1 out of 2 pages.

Unformatted text preview: Name: Student ID: Instructor: Yunus Emre Türkmen 04/10/2015 CHEM 461 Fundamentals of Biochemistry-­‐ Homework 1 (100 points) 1. (40 points) Lone pair-­‐π interaction is another non-­‐covalent interaction that started to attract attention and become popular among chemists within the last decade. Lone pair-­‐π interaction can be viewed as an electrostatic interaction between the lone pair of a donor atom (generally oxygen or nitrogen) and the electropositive π system of an electron-­‐deficient aromatic ring. The strength of this interaction increases as the Lewis base is more electron-­‐rich (more partial negative) and as the electrophilic π system is more electron-­‐deficient (more partial positive). Based on these explanations, rank the following complexes (A-­‐E) with respect to their lone pair-­‐π interaction strengths (strongest: 1, weakest: 5) and explain briefly. OCH3 O CH3 H O N(CH3)2 H O F F N(CH3)2 H O F (H3C)2N N(CH3)2 F F H F O F F H F F F F CH3 F F F 2. (30 points) A researcher wanted to investigate the interaction between A-­‐H and B-­‐ using 1H-­‐NMR spectroscopy (the counter-­‐cation of B-­‐ does not participate in any interaction and can be ignored). For this purpose, she/he recorded the 1H-­‐NMR spectrum of A-­‐H alone (Spectrum 1), and then of a 1:1 mixture of H-­‐A and B-­‐ (Spectrum 2). The chemical shift of A-­‐H proton exhibited a downfield shift in the presence of B-­‐. The researcher thought of two possible explanations for this observation: (1) A hydrogen bonding interaction between A-­‐H and B-­‐; (2) An acid-­‐ base reaction (proton transfer) between A-­‐H and B-­‐. The equations for these two processes are shown below. (Assume that there is no hydrogen bonding interaction between A-­‐ and B-­‐H in the second equation.) A B D C A-H + B- A-H B- (1) A-H + B- A- + B-H (2) E In order to determine which process takes place, the researcher carried out a dilution study. She/he diluted the NMR sample used in the above experiment two-­‐ fold and five-­‐fold, sequentially, and recorded the 1H-­‐NMR spectra of these diluted samples. The NMR spectra of these two diluted samples were found to be the same as the one found in the first experiment (Spectrum 2). Name: 04/10/2015 Student ID: Instructor: Yunus Emre Türkmen Based on the results of the dilution experiments, which one of the processes (1) and (2) do you think takes place? Explain your reasoning in detail. 3. (30 points) Computational studies performed to investigate the anion-­‐π interaction between chloride anion and hexafluorobenzene have shown that the optimal distance between the ring center of hexafluorobenzene and the center of Cl-­‐ is 3.05 Å. ClF F 3.05 Å F F F F A researcher at Bilkent University, Department of Chemistry wants to design a bidentate chloride receptor with two pentafluorophenyl rings attached with an appropriate, symmetrical spacer unit as shown below. By assuming that the electron-­‐deficient rings below have the same optimal distance criterion (3.05 Å) for chloride binding, the researcher aims to calculate the required spacer length, d1. If the distance between the spacer and the ring center is d2, and the angle between the spacer and the pentafluorophenyl group is (90+α)°, then show that d1 can be expressed by the following formula: d1 = 6.10(cosα)-­‐2d2(sinα) The unit of d1 and d2 is Å. d1 SPACER F5 d2 d2 Cl- F5 F5 90+α d1 90+α d2 Cl- F5 ...
View Full Document

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture