Computational Study of Shuangancistrotectorine A …
187
A number of calculations were initially performed using GAUSSIAN 03, Revision
D 01 [20], on desktop computers. At a later stage, the study utilised Gaussian 09,
revision E01 [24] using the CHPC platform.
All the energy values reported in this work are in kcal/mol and all the distances
are in Å. Acronyms are used for the calculation methods and for the media, for conciseness sake on reporting values: HF for HF/6-31G(d,p), DFT for DFT/B3LYP/631+G(d,p), ‘vac’ for vacuum, ‘chlrf’ for chloroform, ‘actn’ for acetonitrile and ‘aq’
for water. Tables with all the numerical values of the properties of the calculated
conformers (relative energies, parameters of the IHBs, dipole moments, free energy
of solvation in the solvents considered, HOMO-LUMO energy gaps, etc.) in the
results of both calculation methods, figures showing all the calculated conformers,
and figures showing comparisons of the SHA results with those of JZM and MCA,
are included in the Electronic Supplementary Information (ESI). The ESI tables and
figures are numbered independently from those included in the text; they may be
cited in the text, and their numbers are preceded by the letter S.
3 Results
3.1 Naming of Conformers
When analysing the results, it is important to recognise the geometric characteristics
of each conformer in an easy way. To this purpose, each conformer is denoted by
an acronym built using symbols (letters) for each of its characterising features. The
O–H···O IHBs and other IHB-type interactions such as O–H···π and C–H···O are
the most important factors stabilizing the conformers, and different conformers have
different IHB patterns. Each IHB or IHB-type interaction is denoted by a specific
lowercase letter in the acronyms. The letters and their meanings are listed in Table 1.
The letters a-h (except ‘e’ and ‘f’) maintain the same meanings as in previous studies
[4–6], i.e., they denote analogous IHBs. The letters ‘i’ and ‘u’ are used to denote types
of C–H···O interactions present in SHA but not in the previously-studied NIQs. The
letters ‘e’ and ‘f’ are excluded from the list in the current study because the IHB-types
that they denoted in previous works [3–6] are not present in SHA.
Each acronym starts with SHA, followed by a number giving a quick idea about
the conformer’s position in the increasing relative energy sequence. The number is
followed by the letters denoting the IHBs present, organised according to the most
common strength-scale of the corresponding IHBs, from stronger to weaker: O–
H···O, O–H···π and C–H···O. Since the mutual orientations of the four moieties also
have significant influence on the energy of the conformers, they are also denoted by
specific letters, listed after those denoting the IHBs; these letters are the same as in
previous works [4–6] and their meaning is explained in Table 1.
187
A number of calculations were initially performed using GAUSSIAN 03, Revision
D 01 [20], on desktop computers. At a later stage, the study utilised Gaussian 09,
revision E01 [24] using the CHPC platform.
All the energy values reported in this work are in kcal/mol and all the distances
are in Å. Acronyms are used for the calculation methods and for the media, for conciseness sake on reporting values: HF for HF/6-31G(d,p), DFT for DFT/B3LYP/631+G(d,p), ‘vac’ for vacuum, ‘chlrf’ for chloroform, ‘actn’ for acetonitrile and ‘aq’
for water. Tables with all the numerical values of the properties of the calculated
conformers (relative energies, parameters of the IHBs, dipole moments, free energy
of solvation in the solvents considered, HOMO-LUMO energy gaps, etc.) in the
results of both calculation methods, figures showing all the calculated conformers,
and figures showing comparisons of the SHA results with those of JZM and MCA,
are included in the Electronic Supplementary Information (ESI). The ESI tables and
figures are numbered independently from those included in the text; they may be
cited in the text, and their numbers are preceded by the letter S.
3 Results
3.1 Naming of Conformers
When analysing the results, it is important to recognise the geometric characteristics
of each conformer in an easy way. To this purpose, each conformer is denoted by
an acronym built using symbols (letters) for each of its characterising features. The
O–H···O IHBs and other IHB-type interactions such as O–H···π and C–H···O are
the most important factors stabilizing the conformers, and different conformers have
different IHB patterns. Each IHB or IHB-type interaction is denoted by a specific
lowercase letter in the acronyms. The letters and their meanings are listed in Table 1.
The letters a-h (except ‘e’ and ‘f’) maintain the same meanings as in previous studies
[4–6], i.e., they denote analogous IHBs. The letters ‘i’ and ‘u’ are used to denote types
of C–H···O interactions present in SHA but not in the previously-studied NIQs. The
letters ‘e’ and ‘f’ are excluded from the list in the current study because the IHB-types
that they denoted in previous works [3–6] are not present in SHA.
Each acronym starts with SHA, followed by a number giving a quick idea about
the conformer’s position in the increasing relative energy sequence. The number is
followed by the letters denoting the IHBs present, organised according to the most
common strength-scale of the corresponding IHBs, from stronger to weaker: O–
H···O, O–H···π and C–H···O. Since the mutual orientations of the four moieties also
have significant influence on the energy of the conformers, they are also denoted by
specific letters, listed after those denoting the IHBs; these letters are the same as in
previous works [4–6] and their meaning is explained in Table 1.