The reported conformers comprise the first fourteen lower-energy conformers and
representative conformers of other types (other combinations of IHBs) not
appearing among the first fourteen. The IHB patterns (numbers and types of IHBs
present in a conformer) are the dominant stabilizing factors. Others factors
influencing conformational preferences are the mutual orientation of the two
naphthalene moieties (C, D and C′, D′ ring systems), which determines the mutual
orientation of the two units (S and S′) and the orientation of the two moieties
(naphthalene and isoquinoline) within each unit. The isoquinoline moiety prefers to
be perpendicular to the naphthalene moiety and the two naphthalene moieties
(linked by the inter-units biaryl axis) also prefer to be perpendicular to each another;
this results in the two units (S and S′) preferring to be mutually perpendicular,
which excludes the possibility of an IHB between them.
As mentioned previously, three types of IHBs interactions may be present:
O−H⋯O IHBs (O43−H52⋯O42 and O44−H54⋯O45), O−H⋯π interactions
between the O−H in an isoquinoline moiety and the closest π system in the
naphthalene moiety of the same unit (O41−H50⋯π, O46−H60⋯π) or between an
O−H in the naphthalene moiety of one unit and the closest π system in the
naphthalene moiety of the other unit (O43−H52⋯π, O44−H54⋯π); and C−H⋯O
interactions within an isoquinoline moiety (C−H49⋯O41 and C−H59⋯O46). The
O−H⋯O IHBs have the strongest stabilizing effect. The two O−H⋯O IHBs (O43
−H52⋯O42 and O44−H54⋯O45) have practically the same geometric parameters
in a conformer having both of them simultaneously.
The lowest energy conformers are the conformers having all the IHB-types
interactions simultaneously. The first five lowest energy conformers have relative
energy below 1.5 kcal/mol in both the HF and the DFT results. They have the same
types of IHBs interactions and differ only by the orientations of the moieties.
Altogether, they account for 99.95% of the population in vacuo (Table S12).
The reported X-ray structure of JZM [3] corresponds to the a-b-f-h-p-v-x conformer, which has 6.269 kcal/mol relative energy and 0.0014 population (Table 2).
This conformer has the two O−H⋯O IHBs (O43−H52⋯O42 and O44
−H54⋯O45), one O−H⋯π interaction and one C−H⋯O interaction. Compared to
the five lowest energy ones (which have all the interactions), this conformer has one
O−H⋯π and C−H⋯O interaction less, which leaves one OH group free. This
phenomenon is observed frequently (e.g., in the case of caespitate [32]): the
crystalline structure differs from the geometry in vacuo by not having one or more
weaker IHBs or other IHB-type interactions that are present in the gas phase.
A possible reason is the need, for molecules in the crystal structure, to have some
donors or acceptors not engaged in intramolecular interactions, so that they are
available for intermolecular interactions with the surrounding molecules.
The symmetry of the molecule results in a number of pairs of conformers with
the same characteristics (IHBs) in the S moiety of one conformer and in the S′
moiety of the other conformer. Pairs of this type will be termed S/S′ symmetric
pairs in the rest of the text.
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M. K. Bilonda and L. Mammino
representative conformers of other types (other combinations of IHBs) not
appearing among the first fourteen. The IHB patterns (numbers and types of IHBs
present in a conformer) are the dominant stabilizing factors. Others factors
influencing conformational preferences are the mutual orientation of the two
naphthalene moieties (C, D and C′, D′ ring systems), which determines the mutual
orientation of the two units (S and S′) and the orientation of the two moieties
(naphthalene and isoquinoline) within each unit. The isoquinoline moiety prefers to
be perpendicular to the naphthalene moiety and the two naphthalene moieties
(linked by the inter-units biaryl axis) also prefer to be perpendicular to each another;
this results in the two units (S and S′) preferring to be mutually perpendicular,
which excludes the possibility of an IHB between them.
As mentioned previously, three types of IHBs interactions may be present:
O−H⋯O IHBs (O43−H52⋯O42 and O44−H54⋯O45), O−H⋯π interactions
between the O−H in an isoquinoline moiety and the closest π system in the
naphthalene moiety of the same unit (O41−H50⋯π, O46−H60⋯π) or between an
O−H in the naphthalene moiety of one unit and the closest π system in the
naphthalene moiety of the other unit (O43−H52⋯π, O44−H54⋯π); and C−H⋯O
interactions within an isoquinoline moiety (C−H49⋯O41 and C−H59⋯O46). The
O−H⋯O IHBs have the strongest stabilizing effect. The two O−H⋯O IHBs (O43
−H52⋯O42 and O44−H54⋯O45) have practically the same geometric parameters
in a conformer having both of them simultaneously.
The lowest energy conformers are the conformers having all the IHB-types
interactions simultaneously. The first five lowest energy conformers have relative
energy below 1.5 kcal/mol in both the HF and the DFT results. They have the same
types of IHBs interactions and differ only by the orientations of the moieties.
Altogether, they account for 99.95% of the population in vacuo (Table S12).
The reported X-ray structure of JZM [3] corresponds to the a-b-f-h-p-v-x conformer, which has 6.269 kcal/mol relative energy and 0.0014 population (Table 2).
This conformer has the two O−H⋯O IHBs (O43−H52⋯O42 and O44
−H54⋯O45), one O−H⋯π interaction and one C−H⋯O interaction. Compared to
the five lowest energy ones (which have all the interactions), this conformer has one
O−H⋯π and C−H⋯O interaction less, which leaves one OH group free. This
phenomenon is observed frequently (e.g., in the case of caespitate [32]): the
crystalline structure differs from the geometry in vacuo by not having one or more
weaker IHBs or other IHB-type interactions that are present in the gas phase.
A possible reason is the need, for molecules in the crystal structure, to have some
donors or acceptors not engaged in intramolecular interactions, so that they are
available for intermolecular interactions with the surrounding molecules.
The symmetry of the molecule results in a number of pairs of conformers with
the same characteristics (IHBs) in the S moiety of one conformer and in the S′
moiety of the other conformer. Pairs of this type will be termed S/S′ symmetric
pairs in the rest of the text.
314
M. K. Bilonda and L. Mammino