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Introduction

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Structures should be oriented horizontally

In general, structures should be oriented so that their main axis is horizontal

RECOMMENDED

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However, this guideline is intended for structures whose longest axis is significantly longer than their shortest axis. In cases where the longest and shortest axes of a structure are more nearly the same size, it is common for the structure to have a preferred vertical orientation. These cases will be discussed further in subsequent sections.

RECOMMENDED	RECOMMENDED	AVOID	AVOID

Large ring systems should be in standard orientation

If the structure features a ring system containing at least two fused rings, that system should be presented in its preferred orientation. For most practical purposes, it is sufficent to orient the ring system so that:

• The fused ring system is oriented more or less horizontally
• If the system contains multiple "rows" of rings, any "extra" rings should be positioned so that they are towards the right and the top of the ring system
• Larger rings should be toward the left and smaller rings toward the right
• Heteroatoms should be toward the right and, with slight preference, toward the bottom

These guidelines intentionally differ from the Nomenclature of Fused and Bridged Fused Ring Systems. Those guidelines should be used to number the atoms within a fused ring system, but these should be used when depicting that ring system after its atoms have been numbered.

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RECOMMENDED	RECOMMENDED	AVOID	AVOID

Principal groups should be toward the right

Any principal group(s), if present, should be oriented toward the right side of the structure. In a perfect application of this guideline, principal groups would be identified using the comprehensive hierarchical guidelines provided in other IUPAC recommendations [need to add references]. For most practical purposes, it is sufficient to treat "principal groups" and "acyclic heteroatoms" as synonymous. Thus, this rule could be oversimplified to say that any acyclic heteroatoms should be oriented toward the right side of the structure.

Since systematic numbering starts nearest the principal group(s), this guideline also implies that structures should be oriented so that systematic numbering increases from right to left within the structure.

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AVOID	AVOID	AVOID	AVOID

Rings should be toward the bottom-left

In the absence of a different overriding concern, the largest ring system within a structure should be oriented toward the bottom-left of the structure.

RECOMMENDED	AVOID	AVOID	AVOID

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Symmetry is good

In the absence of a different overriding concerns, diagrams that highlight the symmetry of symmetric structures (or portions of structures) are preferred to those that don't.

RECOMMENDED	AVOID