The crystal structures of monoclinic 5-ethylbarbituric acid and 5-hydroxy-5-ethylbarbituric acid

Abstract

The crystal data for the two forms of 5-ethylbarbituric acid (EBA) are (I) monoclinic (m.p. 194--196°), a= 11.151, b =6.838, c= 9.536 A, fl= 92°21 ', space groupP2)/c with four, molecules per cell; (II)triclinic (m.p. 142-145 ), a=6.018, b= 5.344, c= 12.121/~, ~=93 38, fl= 105 42, ),=94 19, space group P1 or PT with two molecules per cell. The crystal structure of (I) is reported together with that of the oxidation product 5-hydroxy-5-ethylbarbituric acid (HEBA) which is monoclinic (m.p. 207-209°), a= 10.088, b = 6.298, c = 11-914 A, fl= 99 36", space group P2t/n with four molecules per cell. The X-ray diffraction data (Cu K~ radiation) were obtained using an automatic four-circle diffractometer. All hydrogen atoms were found in difference Fourier syntheses. Full-matrix least-squares refinement gave R values of 0-06 and 0.05 respectively. The rings in both EBA and HEBA have a 'flap' conformation with C(5) displaced from an otherwise nearly flat ring. In EBA the ethyl group is equatorial, while in HEBA it is axial. All NH and OH hydrogen bond donor groups form hydrogen bonds. The acidic hydrogen atom H(5) in EBA is not hydrogen bonded. The non-hydrogen-bonded carbonyl oxygen atom 0(6) makes close approaches (2.93 and 3.04/~) to carbonyl carbon atoms C(4) and C(6) of an adjacent molecule.

Crystal structure of flavonoid compounds. I. 4'-Bromoflavanone

“…, is 1.230 (7)A which is close to that of 1.220 A in barbiturates (Gatehouse & Craven, 1971) and the value in International Tables for X- (iii) Molecular packing Significant non-bonded interactions are given in Table 7 where those listed are not more than 0.3 A longer than those given by Pauling (1960) and by Bondi (1964). Fig.…”

Hydrogen bonding NH...O = C of barbiturates: the (1:1) crystal complex of urea and 5,5-diethylbarbituric acid (barbital)

“…Crystal structure (a) Barbituric acids 5,5-Diethylbarbituric acid (barbital), form I (Craven, Vizzini & Rodrigues, 1969) Barbital, form II (Craven, Vizzini & Rodrigues, 1969) Barbital, form IV (Craven & Vizzini, 1971) 5-Ethyl-5-isoamylbarbituric acid (amobarbital), form I 2-89 Amobarbital, form II 2.91, 2.86 5-Ethyl-5-(3,3-dimethylbutyl)barbitutic acid (Gartland & Craven, 1971) 2.82 5-Ethyl-5-(1-methylbutenyl)barbituric acid (Craven & Cusatis, 1969) 2.87, 2.92 5-Ethyl-5-butylbarbituric acid (Bideau, 1971) 2.86 5-Ethyl-5-(1-cyclohexen-l-yl)barbituric acid (Bideau & Artaud, 1970) 2.87 5-Ethyl-5-(1-cyciohepten-l-yl)barbituric acid (Bideau, Leroy & Housty, 1969) 2"89, 2.87 5-Ethyl-5-phenylbarbituric acid, form III (Williams, 1974) 2.89, 2-91 5-Methyl-5-phenylbarbituric acid (Bravic, Housty & Bideau, 1968) 2.90 5-Ethylbarbituric acid (Gatehouse & Craven, 1971) 2.85 (b) 1-Methylbarbituric acids 1-Methyl-5,5-diethylbarbituric acid (Wunderlich, 1973) 2"84 1-Methyl-5-ethyl-5-(l-cyclohexen-l-yl)barbituric acid (Bideau, Leroy & Housty, 1970) 2"88 1-Methyl-5-ethyl-5-phenylbarbituric acid (Bideau, Marly & Housty, 1969) 2.89 (c) Barbiturate anions Sodium barbital (Berking & Craven, 1971) 2.84 Calcium barbital trihydrate (Berking, 1972) Guanidinium barbital dihydrate (McClure & Craven, 1973) (Craven & Gartland, 1970) 2.98, 2.94, 2.93 -5,5-Diethylbarbituric acid/aminopyrine (1 : 1) (Kiryu, 1971) 2.82 2"75 5,5-Diethylbarbituric acid/urea (1:1) (This paper) -2.78, 2-80 5,5-Diethylbarbituric acid/acetamide) (1:1) (Hsu & Craven, 1974a) -2"82, 2-82 5-Ethyl-5-isoamylbarbituric acid/salicylamide (1 : 1) (Hsu & Craven, 1974b) 2.92 -5,5-Diethylbarbituric acid/imidazole (1:1) (Hsu & Craven, 1974c) 2.91 - The shortest reported distances which we could find were 2-55/~ in cysteylglycine sodium iodide (Dyer, 1951) and 2.621~ in guanine hydrochloride monohydrate (Broomhead, 1951). Since these structure determinations were based only on zonal X-ray intensity data, a more reliable lower limit for N...O distances might be 2.67 A which occurs in the urea/ parabanic acid complex …”

Crystal Structure and Conformation of a Dipyrrylmethane. The gem-Dimethyl Effect

“…3) also unconventionally orients the NHs syn to the gem-dimethyl group, leaving the C(18) and C (19) methyls buttressed against one another. The apparently shortened sp 3 -sp 3 bonds of the ethyl ester groups are ascribed to the neglect of the relatively large thermal motion, as seen in the ethyl groups of 2 [13] and in certain ethyl-barbituric acid derivatives [21]. As in 2, the two pyrrole rings of 1 are virtually equivalent with respect to bond lengths and bond angles (Fig.…”