3 Results
3.1 Results in Vacuo
The major factors influencing the conformational preferences of MUCH-B are the
IHB patterns, i.e. the number and types of IHBs present in the conformer, and
the orientations of the two benzene rings, both mutually and with respect to the
xanthone moiety. Seven IHBs are possible (not all simultaneously, but up to four
simultaneously): H23⋯O17, H25⋯O17, H25⋯O19, H26⋯O19, H26⋯O21,
H28⋯O21 and H23⋯O41 (the atom numbering utilised in this work is shown in
Fig. 1). H23⋯O41 is the only possible IHB between the two moieties, as only O41,
being in ortho to C15, can come close enough to the xanthone moiety to engage in
an IHB.
Because of the importance of the IHBs, the IHB pattern is selected as the first
criterion to classify the conformers. Therefore, conformers are denoted with a
number referred to their IHB pattern, as shown in Table 1 and illustrated in Fig. 2,
followed by a letter. The letter is progressive according to the relative energy of the
1-type conformers and remains associated with similar orientation of the A and B
rings with respect to the xanthone moiety for the 3-, 5-, 6-, 9- and 11-type conformers (conformers not having the H23⋯O41 IHB). For the conformers with the
H23⋯O41 IHB (2-, 4-, 7-, 8- and 10-type), two orientations of the A and B rings
are possible without disrupting this IHB, and they are denoted with the letters a and
b, independently of the use of these letters for the conformers not having the
H23⋯O41 IHB. Table 2 shows the relative energies of the calculated conformers in
the results of all the methods utilised in vacuo and, for the DFT/B3LYP/6-31+G(d,
p) level, also in all the solvent considered. Figure 3 shows the geometries of most of
the conformers.
The mutual orientation of the three moieties can remarkably influence the
conformers’ energy. For instance, among the conformers with the most favourable
Table 1 Combinations of intramolecular hydrogen bonds (IHB) in the conformers of
muchimangin B and numbers utilised to denote them in the conformers’ names
Conformer
number
IHB present
H23⋯O17 H25⋯O17 H25⋯O19 H26⋯O19 H23⋯O41 H26⋯O21 H28⋯O21
1
x
x
x
x
2
x
x
x
x
3
x
x
x
4
x
x
x
x
5
x
x
x
x
6
x
x
x
x
7
x
x
x
8
x
x
x
x
9
x
x
x
10
x
x
x
x
1 1
x
x
x
x
Ab-Initio and DFT Study of the Muchimangin-B Molecule
95
3.1 Results in Vacuo
The major factors influencing the conformational preferences of MUCH-B are the
IHB patterns, i.e. the number and types of IHBs present in the conformer, and
the orientations of the two benzene rings, both mutually and with respect to the
xanthone moiety. Seven IHBs are possible (not all simultaneously, but up to four
simultaneously): H23⋯O17, H25⋯O17, H25⋯O19, H26⋯O19, H26⋯O21,
H28⋯O21 and H23⋯O41 (the atom numbering utilised in this work is shown in
Fig. 1). H23⋯O41 is the only possible IHB between the two moieties, as only O41,
being in ortho to C15, can come close enough to the xanthone moiety to engage in
an IHB.
Because of the importance of the IHBs, the IHB pattern is selected as the first
criterion to classify the conformers. Therefore, conformers are denoted with a
number referred to their IHB pattern, as shown in Table 1 and illustrated in Fig. 2,
followed by a letter. The letter is progressive according to the relative energy of the
1-type conformers and remains associated with similar orientation of the A and B
rings with respect to the xanthone moiety for the 3-, 5-, 6-, 9- and 11-type conformers (conformers not having the H23⋯O41 IHB). For the conformers with the
H23⋯O41 IHB (2-, 4-, 7-, 8- and 10-type), two orientations of the A and B rings
are possible without disrupting this IHB, and they are denoted with the letters a and
b, independently of the use of these letters for the conformers not having the
H23⋯O41 IHB. Table 2 shows the relative energies of the calculated conformers in
the results of all the methods utilised in vacuo and, for the DFT/B3LYP/6-31+G(d,
p) level, also in all the solvent considered. Figure 3 shows the geometries of most of
the conformers.
The mutual orientation of the three moieties can remarkably influence the
conformers’ energy. For instance, among the conformers with the most favourable
Table 1 Combinations of intramolecular hydrogen bonds (IHB) in the conformers of
muchimangin B and numbers utilised to denote them in the conformers’ names
Conformer
number
IHB present
H23⋯O17 H25⋯O17 H25⋯O19 H26⋯O19 H23⋯O41 H26⋯O21 H28⋯O21
1
x
x
x
x
2
x
x
x
x
3
x
x
x
4
x
x
x
x
5
x
x
x
x
6
x
x
x
x
7
x
x
x
8
x
x
x
x
9
x
x
x
10
x
x
x
x
1 1
x
x
x
x
Ab-Initio and DFT Study of the Muchimangin-B Molecule
95