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Formula Hierarchy

Description

The Formula Hierarchy consists of a series of levels. Level 1 lists molecular formulas that lead, through subsequent levels, to specific substance names.

Substance names in the hierarchy are organized by chemical structure. Each successive level in the hierarchy adds more chemical name information.

The molecular formula of each substance cited in a reference on CA on CD is listed in the Formula Hierarchy.

Diagram

The following diagram shows three levels in the Formula Hierarchy for Benzoic acid: molecular formula = C7H6O2.

Path History

The path that is followed through the hierarchy is shown at the top of the window. It is represented as a sequential list of hierarchy entries, preceded by minus signs. Each item in the path history indicates a previously visited level in the current path.

Level 1

Level 1 lists molecular formulas in alphabetic order.

Element symbols in molecular formulas are arranged according to the Hill System. 

Type of compound	Hill System	Example
Carbon containing compounds	C first, H next (if present), then the remaining element symbols alphabetically	C11H16FNO2
Compounds that do NOT contain carbon	Alphabetically by element symbols	BiFeO3

Level 2

Level 2 lists the principal portion of substance names associated with a Level 1 molecular formula (MF). Level 2 names have locants removed and are arranged in alphabetic order. Numeric entries, if present, are listed first.

Level 2 names are for substances	Example Level 1 MF = C7H6O2
	Level 2 name	Level 2 name leads to
Which have the Level 1 MF	Benzodioxole	1,3-benzodioxole (MF = C7H6O2)
Whose substituted form has the Level 1 MF	Benzaldehyde	4-hydroxybenzaldehyde (MF = C7H6O2)
Which are components of multicomponent substances, of which one of the components has the Level 1 MF	Acetaldehyde	Acetaldehyde polymer with 4-hydroxybenzaldehyde (MF = C7H6O2) and 3-methylphenol

Level 3

Substance names in Level 3 have locants added (if any).

Subdivision Headings indicate how substances are grouped in the next level of the hierarchy:

• QUALIFIED
• SUBSTITUTED
• MODIFIED
• STEREO

Subdivision Headings

Subdivision Headings are used to organize substance information.

Subdivision Heading	This heading is used	Explore this subdivision to find
QUALIFIED	With commonly occurring substances that historically have many references	Links to references about the substance grouped by "type of study" "type of modification"
SUBSTITUTED	When there are substituted forms of the substance	A form of the substance in which a hydrogen is replaced by another atom
MODIFIED	When a nonQUALIFIED substance has a modified form	A modified form of the substance such as a Derivative Isotope Ion
STEREO	When the structure has stereochemical specificity	A particular stereochemical isomer such as R or S D or L Cis or trans

Other Levels

The content of the hierarchy, beyond Level 3, varies with the substance and the path that is followed.

The types of entries contained in a level depend on which Subdivision Heading is followed.

If the Subdivision Heading followed is	Then, nested entries are for
QUALIFIED	The "type of study" in which the substance was used or modified forms of the substance
SUBSTITUTED MODIFIED STEREO	Substance names with additional chemical specificity

Example: QUALIFIED Entries

The bottom window in this example shows the entries nested within Benzoic acid (QUALIFIED).

Example: SUBSTITUTED Entries

The bottom window in this example shows the entries nested within Benzoic acid (SUBSTITUTED).

Navigation Order

When a chemical substance fits under more than one Subdivision Heading, navigate the Substance Hierarchy in the following order:

If you are interested in	Then, follow	Example
The substance	The QUALIFIED heading to find links to references grouped by "type of study"	Follow Butanoic acid (QUALIFIED)[107-92-6] analysis to locate studies on the analysis of butanoic acid
A multi component substance, where one component is a QUALIFIED substance	1. The QUALIFIED heading 2. The "type of modification" heading	Follow Butanoic acid (QUALIFIED)--compounds (MODIFIED) to locate a multi component substance containing the QUALIFIED substance
A nonspecifically modified form of the substance	The QUALIFIED heading to find links to references grouped by type of nonspecific modification	Follow Butanoic acid (QUALIFIED)[107-92-6] esters to locate studies on nonspecific esters of butanoic acid