Emily F. Maverick

Hydrogen bonding and π-stacking in dipyrrinone acid dimers of xanthobilirubic acid and chiral analogs

Abstract Xanthobilirubic acid and its analogs self-associate strongly through intermolecular hydrogen bonding between their carboxylic acid and dipyrrinone components, forming π-stacked dimers. In contrast, their methyl esters form planar dimers conjoined by dipyrrinone to dipyrrinone intermolecular hydrogen bonding. When a stereogenic center is present in the propionic side acid chain, unusually large optical rotations and exciton coupling circular dichroism may be observed for the optically active acids: βS -methylxanthobilirubic acid ( 1 ) has [ α ] D 20 = −314° and Δ ∈ 434 max = −10.9, Δ ∈ 388 max = +5.7 (CHCl 3 ). In contrast, methyl esters show weaker rotations and vanishingly small CD: the methyl ester of ( 1 ) has [ α ] D 20 +62° and Δ ∈ 435 ⪡ 0.5, Δ ∈ ⪡ 0.5.

Characterization of cavities in carcerands

CPK models, originally derived from crystal structure results, have guided the design of complexing partners with a wide range of properties. The complexes presented here associate in organic media, a process which is usually entropy-opposed; some of the velcraplexes however are entropy-driven. Unless the partners are highly preorganized for complexation, crystal structures may not reflect the molecules in solution.

Hemicarcerands containing tosylamide bridges

Two new hemicarcerand hosts with tosylamide bridges are found to be relatively selective binders. The tosyl groups could not be removed without destroying the hosts. A crystal structure of the smaller host suggests that two of the four 28-membered ring portals are rigidly locked in an open position.

The tert-butylammonium perchlorate complex of 2,3-naphtho-18-crown-6 at 115 K.

In the title complex, tert-butylammonium perchlorate-2,5,8,11,14,17-hexaoxatricyclo[16.8.0.0(20,25]hexac osa- 1(26),18,20(25),21,23-pentaene-ethyl acetate-dichloromethane (4/4/1/1), C4H12N+.C20H26O6.ClO4-.0.25C4-H8O2.0.25CH2Cl2 , the tert-butylammonium cation binds to the macrocyclic host (Chemical Abstracts name: 2,3,5,6,8,9,11,12,14,15-decahydro-1,4,7,10,13,16-hexaoxanaphtho [2,3- b]cyclooctadecin) in the expected tripod arrangement, while the perchlorate anion links naphthyl groups in the crystal through C-H...O-Cl-O...H-C interactions. Thermal motion analysis indicates that the tert-butylammonium group and the perchlorate anion each librate with respect to the host, with amplitudes of 6.2 (4) and 11.4 (2) degrees, respectively.

Thermal motion of tert‐butyl groups III. tert‐Butyl substituents in aromatic hydrocarbons, the view from the bottom of the well

The rigidity of the tert-butyl group (TBG) as a substituent in aromatic hydrocarbons is investigated, with a modified Hirshfeld test of anisotropic displacement parameters (ADPs) as a primary criterion. Four new structures are analyzed, along with low-temperature studies of a previously published crowded supermesityl dimer; three of the five structures meet the primary test. Most of the TBGs meet the Hirshfeld test at 100 K, and the ADPs are improved by omitting low-order data in the final refinement. The three most precise structures yield a wide variation in libration amplitudes (and in estimated rotation barriers) for 13 unique TBGs. A similar range of values is found in analyses of structures in the Cambridge Crystallographic Database. The libration amplitudes are calculated with the program THMA14C, with each TBG as an attached rigid group (ARG). Packing analysis suggests that large ADPs, especially for some individual TBG methyl groups, correspond to voids in the crystal. Published barriers to TBG reorientation, determined by solid-state NMR spin-lattice relaxation methods, for six related crystalline compounds are compared with barriers calculated from their crystal structure data.

Three Complexes of a [2.2]Cryptahemispherand

The macrocyclic host 36,37,38-trimethoxy-5,10,15-trimethyl-22,25,30,33-tetraoxa-1,19-diazapentacyclo-[17.8.8.1 3,7 ,1 8,12 ,1 13,17 ] octatriaconta-3,5,7(36),8,10,12(37),13,15,17(38)-nonaene contains a somewhat flexible cavity lined with seven O atoms and two N atoms. The structures of three of its complexes are reported here: that with sodium thiocyanate, (I) ([Na(C 38 H 52 N 2 O 7 )]SCN}, at 296 K, and those with potassium thiocyanate, (II) ([K(C 38 H 52 N 2 O 7 )]SCN.H 2 O}, and caesium perchlorate, (III) {[Cs(C 38 H 52 N 2 O 7 )]ClO 4 .H 2 O}, at 156 K. The host adapts well to Cs + , with effective ninefold coordination; it adapts nearly as well to K + , but is not sufficiently flexible to be a good complexer for the much smaller Na + ion. In structures (II) and (III), a water molecule forms hydrogen bonds between an O atom of the host and an atom of the anion [N of SCN in (II) and O of ClO 4 - in (III)].

Additions and corrections: host-guest complexation. 38. Cryptahemispherands and their complexes.

Nucleophilic Activation of Coordinated Carbon Monoxide. 3. Hydroxide and Methoxide Reactions with the Trinuclear Clusters MJ(C0)12 ( M = Fe, Ru or Os). Implications with Regard to Catalysis of the Water Cas Shift Reaction [J. Am. Chem. SOC. 1985, 107, 585-5933. DAVID C. GROSS and PETER C. FORD* Page 592: The two equations appearing in the right-side column of print are incorrect. These should be respectively

A hemispherand containing cyclic urea and anisyl units and its 1:1 (CH3)3CNH3+ complex

26,27-Dimethoxy-4,18-dimethyl-8,11,14-trioxa1,21-diazatetracyclo[ 19.3.1.12,6.116,2°]heptacosa2,4,6 (26), 16,18,20(27)-hexaen-25-one, C 26 H 34N206, (1), M r = 4 7 0 . 5 7 , orthorhombic, P2~2~2,, a = 10.124(4), b = 1 1 . 9 6 4 ( 4 ) , c = 2 1 . 3 1 7 ( 5 ) / ~ , V = 2582 (2) A 3, Z = 4 , D x=1.21gcm -3, 2(MoK~t)= 0.7107A, # = 0 . 8 0 c m -~, F (000)= 1008.4, T = 295 K, R-----0-106 for 1956 observed reflections. The complex of (1) with (CH3)3CNH+.CIO~, C26Ha4N 2O6.CaHI2N+.CIO4, (2), M r = 6 4 4 . 1 6 , orthorhombic, Fdd2, a = 46.037 (9), b = 25.930 (4), c = 10.900 (2)/k, V-13012 (2) A 3, Z = 16, Dx= 1.32 g cm -a, 2(Cu K~t) = 1.5418 A, # = 14.4 cm -~, F ( 0 0 0 ) 5 5 2 6 . 6 , T = 115 K, R = 0 . 0 6 0 for 2277 observed reflections. In the free host (1), the three O atoms of the O(CH2CH20)2 bridge are turned outward, with some --CH 2groups turned inward. The host in (2) has been reorganized by the perching interaction of the tert-butylammonium ion; all the O atoms of the bridge now turn inward, two of them being hydrogenbonded to the cation, which is also hydrogen-bonded to the urea O atom of the host. Introduction. Hemispherands are hosts for which at least half of the cavity is organized for complexation during synthesis rather than during binding (Cram & Trueblood, 1981). This hemispherand, containing one urea unit and two anisyl units (shown below) is a much better binder of tert-butylammonium ion but a somewhat poorer binder for alkali metal ions and NH4 + than is the similar hemispherand that contains three anisyl units (Cram, Dicker, Lein, Knobler & Trueblood, 1982).