Antagonistic Interplay Between an Intermolecular CH···O and an Intramolecular OH···O Hydrogen Bond in a 1:1 Complex Between 1,2-Cyclohexanedione and Chloroform: A Combined Matrix Isolation Infrared and Quantum Chemistry Study

Abstract

Matrix isolation infrared spectra of a weak C-H···O hydrogen-bonded complex between the keto-enol form of 1,2-cyclohexanedione (HCHD) and chloroform have been measured. The spectra reveal that the intramolecular O-H···O H-bond of HCHD is weakened as a result of complex formation, manifesting in prominent blue shift (∼23 cm) of the ν band and red shifts (∼7 cm) of ν bands of the acceptor (HCHD). The ν band of donor CHCl undergoes a large red shift of ∼33 cm. Very similar spectral effects are also observed for formation of the complex in CCl solution at room temperature. Our analysis reveals that out of several possible iso-energetic conformational forms of the complex, the one involving antagonistic interplay between the two hydrogen bonds (intermolecular C-H···O and intramolecular O-H···O) is preferred. The combined experimental and calculated data presented here suggest that in condensed media, conformational preferences are guided by directional hyperconjugative charge transfer interactions at the C-H···O hydrogen bonding site of the complex.

DFT Study To Explore the Importance of Ring Size and Effect of Solvents on the Keto–Enol Tautomerization Process of α- and β-Cyclodiones

“…The experimental results corroborate keto–enol formation in cyclohexane-1,2-dione. 64,66 The M062X-SMD aq /6-31+G(d,p)-calculated activation free energy barrier for cyclohexane-1,2-dione ( 4 ) is 67.3 kcal/mol. An alkyl substitution in the ring system can improve the enol formation in cyclohexane-1,2-diketone.…”

“…63 Tautomerization of 1,2-cyclohexanedione has also been examined computationally and experimentally. 64−66 There are also reports on direct α-alkylation of 1,2-cyclohexanedione and its enolization, which occurs via its dianionic form. 67,68 Keto–enol tautomerization of cyclic-α-diketones and cyclic-β-diketones has been studied by many research groups; however, the effects of ring size on the keto–enol tautomerization process and the role of solvents on such systems have not been explored in the literature.…”

Controllable Synthesis of a Highly Ordered Polymeric Structure Assembled from Cobalt‐Cluster‐based Racemic Supramolecules

“…The presence of the hydroxyl group on HIP is criticalf or the formation of intermolecular hydrogen bonds, and couldi nfluence the crystal packing of 2.T he average distance between hydrogen and carboxylate atoms (H29···O16 and H39···O24) is approximately 1.949 ,s uggesting the presence of intermolecular hydrogen bonds between supramolecules in solid-state. [17] The O29···O16 and O39···O24 distances are 2.663 and 2.619 ,r espectively.T he O29-H29···O16a nd O39-H39···O24 angles are 129.3 and 151.58,r espectively.A ss een in Figure 4c,t wo inter- molecular hydrogen bonds form betweent wo neighborings upramolecules with different conformations( displayed in different colors), which may accountf or their parallel arrangement. On the other hand, only one hydrogen bond forms between racemic supramolecules (presented with the same color in Figure 4c).…”

“…[16] As seen in the inset of Figure 3a,h ydrogen atoms (H29) from ah ydroxyl groups (O29) from one polymeric strand of 1 and carboxylate oxygen atoms (O16) from the neighboringo ne are within an acceptable range for hydrogen bond (inset in Figure 3a), with the O29···O16 distance and O29-H29···O16 angle of approximately 2.271 and 168.88,r espectively. [17] It shoulda lso be noted that the intermolecular hydrogen bonds are only formed between left-handed and right-handed supramolecules from each adjacent strand. On this basis, we speculate that the hydroxyl groups and their respective intermolecular hydrogen bonds play av ital role in the solid-state packing of 1.…”

Simultaneous exhibition of positive and negative cooperativity by purely C-H—O H-bonded (1,3-cyclohexanedione)n (n = 2-6) clusters: A density functional theoretical investigation

“…Over the last couple of decades, however, various classes of weak H-bonding interactions have been found to play important roles in dictating structures, and consequently functions, of biological macromolecules 35,36,37, Cooperative effects imparted by neighboring H-bonds, either classical or weak, on these bonds, and also in the reverse direction, inside the macromolecules are expected to provide appreciable impetus in their extra stabilization. This has prompted several studies on cooperativity involving weak Hbonds, a few of them dealing with negative cooperativity as well 38,39,40,41,42,43,44 . Nevertheless, most of these studies, that include both experimental 45,17,46,47,48 and theoretical 49,50,51,52,53 works, have dealt with how a weak H-bond cooperatively stabilizes (or destabilizes) a classical H-bond in either inter-or intra molecular fashion.…”