Syntax cheat sheet

A single-page reference for every construct AsciiChem can encode. Print it, bookmark it, or scan it before writing chemistry.

Elements and atoms

Construct	Syntax	Example	Notes
Element symbol	Capital + optional lowercase	H, He, Fe	One or two letters
Subscript (multiplicity)	_N after atom	H_2, H_2O	Binds to preceding atom
Multi-char subscript	_{...}	H_{2a}	Braces for non-numeric
Stoichiometric coefficient	Leading digits	2H_2O, 3H_2	Distinct from subscript

Source Rendered

H He H_2 H_2O C_6H_12O_6 2H_2O

$\mathrm{H}\mathrm{He}{\mathrm{H}}_2{\mathrm{H}}_2\mathrm{O}{\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_{6}2{\mathrm{H}}_2\mathrm{O}$

Isotopes and charge

Construct	Syntax	Example	Notes
Prefix isotope	^N before atom	^14C, ^238U	Binds to following atom
Charge (suffix)	^N± after atom	Ca^2+, Cl^-	IUPAC number-then-sign
Oxidation state	^(Roman)	Fe^(II), Mn^(VII)	Roman numerals in parens

Source Rendered

^14C ^131I ^238U Ca^2+ Cl^- SO_4^2- Fe^(II) Fe^(III)

${}^{14}\mathrm{C}{}^{131}\mathrm{I}{}^{238}\mathrm{U}{\mathrm{Ca}}^{2+}{\mathrm{Cl}}^{-}\mathrm{S}{\mathrm{O}}_4^{2-}{\mathrm{Fe}}^{\mathrm{II}}{\mathrm{Fe}}^{\mathrm{III}}$

The headline semantic fix

^14C binds the isotope to the atom — one Atom with isotope: "14". AsciiMath would produce an empty phantom base followed by the atom, losing the binding entirely.

Groups (parenthesised sub-formulae)

Bracket	Syntax	Example
Parentheses	(...)	Ca(OH)_2
Square brackets	[...]	[Fe(CN)_6]
Braces	{...}	{NH_4}_2SO_4

Bracket kind is preserved through round-trip — () stays (), [] stays [].

Source Rendered

Ca(OH)_2 (NH_4)_2SO_4 [Fe(CN)_6] [Fe(CN)_6]_3

$\mathrm{Ca}{\left(\mathrm{O}\mathrm{H}\right)}_2{\left(\mathrm{N}{\mathrm{H}}_4\right)}_2\mathrm{S}{\mathrm{O}}_4\left[\mathrm{Fe}{\left(\mathrm{C}\mathrm{N}\right)}_6\right]{\left[\mathrm{Fe}{\left(\mathrm{C}\mathrm{N}\right)}_6\right]}_3$

Bonds (8 kinds)

Kind	Syntax	Example	CML order
Single	-	H-O-H	S
Double	=	H_2C=CH_2	D
Triple	#	HC#CH	T
Quadruple	##	Re##Re	Q
Wedge (toward viewer)	>-	C>-H	W
Hash (away from viewer)	-<	C-<H	H
Dative / coordinate	~>	NH_3~>BF_3	DG
Wavy / resonance	~~	A~~B	V

Source Rendered

H-O-H H_2C=CH_2 HC#CH Re##Re C>-H C-<H NH_3~>BF_3 A~~B

$\mathrm{H}-\mathrm{O}-\mathrm{H}{\mathrm{H}}_2\mathrm{C}=\mathrm{C}{\mathrm{H}}_2\mathrm{H}\mathrm{C}\equiv \mathrm{C}\mathrm{H}\mathrm{Re}≣\mathrm{Re}\mathrm{C}\uparrow \mathrm{H}\mathrm{C}\downarrow \mathrm{H}\mathrm{N}{\mathrm{H}}_3\to \mathrm{B}{\mathrm{F}}_3\mathrm{A}\sim \mathrm{B}$

Why ~> for dative?

The -> sequence is already the reaction arrow. ~> was chosen to avoid collision while evoking the donation direction of a coordinate bond.

Stereochemistry

Construct	Syntax	Example
R/S configuration	(R)-, (S)-	(R)-CH_3, (S)-CH(OH)COOH
E/Z geometry	(E)-, (Z)-	(E)-CH=CH, (Z)-A=B
Greek alpha/beta	(alpha)-, (beta)-	(alpha)-C, (beta)-C
Greek Unicode	(α)-, (β)-	(α)-C

AsciiMath-style typed words (alpha, beta) are accepted alongside the Unicode symbols.

Source Rendered

(R)-CH_3 (S)-CH(OH)COOH (E)-CH=CH (Z)-A=B (alpha)-C (beta)-C

$\text{(R)-}\mathrm{C}{\mathrm{H}}_3\text{(S)-}\mathrm{C}\mathrm{H}\left(\mathrm{O}\mathrm{H}\right)\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}\text{(E)-}\mathrm{C}\mathrm{H}=\mathrm{C}\mathrm{H}\text{(Z)-}\mathrm{A}=\mathrm{B}\text{(alpha)-}\mathrm{C}\text{(beta)-}\mathrm{C}$

Lewis structures

Construct	Syntax	Example	Meaning
Lone pair prefix	: or ::	:O, ::O	1 or 2 lone pairs
Radical suffix	.	Cl., O=O..	Unpaired electron(s)

Source Rendered

:O ::O Cl. O=O..

$\text{:}\mathrm{O}\text{::}\mathrm{O}\mathrm{Cl}\text{.}\mathrm{O}=\mathrm{O}\text{..}$

Reactions

Arrow	Syntax	Kind	Example
Forward	->	:forward	2H_2 + O_2 -> 2H_2O
Reverse	<-	:reverse	A <- B
Equilibrium	<=>	:equilibrium	N_2 + 3H_2 <=> 2NH_3
Resonance	<->	:resonance	A <-> B

Conditions (above/below the arrow)

Conditions sit in bracketed groups immediately after the arrow. The first [...] is the above condition (catalyst); the second is the below condition (temperature, pressure).

Source Rendered

N_2 + 3H_2 <=>[Fe][400C] 2NH_3 A <=>[H_2O] B

${\mathrm{N}}_2+3{\mathrm{H}}_2\underset{\mathrm{Fe}}{\overset{400\mathrm{C}}{\rightleftharpoons }}2\mathrm{N}{\mathrm{H}}_3\mathrm{A}\stackrel{{\mathrm{H}}_2\mathrm{O}}{\rightleftharpoons }\mathrm{B}$

Reaction cascades (multi-step)

Source Rendered

A -> B -> C 2A -> 2B -> 2C A <=>[Fe][T] B -> C

$\mathrm{A}\to \mathrm{B}\to \mathrm{C}2\mathrm{A}\to 2\mathrm{B}\to 2\mathrm{C}\mathrm{A}\underset{\mathrm{Fe}}{\overset{\mathrm{T}}{\rightleftharpoons }}\mathrm{B}\to \mathrm{C}$

Multi-step chains promote to a single ReactionCascade.

Electron configurations

Two or more orbital^occupancy pairs:

Source Rendered

1s^2 2s^2 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10

${\mathrm{1s}}^2 {\mathrm{2s}}^2 {\mathrm{1s}}^2 {\mathrm{2s}}^2 {\mathrm{2p}}^6 {\mathrm{3s}}^2 {\mathrm{3p}}^6 {\mathrm{4s}}^2 {\mathrm{3d}}^{10}$

Ground state of zinc.

Embedded mathematics

Backtick-delimited runs are parsed by Plurimath:

Source Rendered

`K_c = [P]/[R]` `x^2 + y^2` `rate = k[A]^2[B]`

${\displaystyle K_c=\frac{P}{R}}{\displaystyle x^2+y^2}{\displaystyle rate=k{\left[A\right]}^2\left[B\right]}$

Use embedded math for equilibrium constants, rate laws, and thermodynamic expressions that sit naturally inside chemistry.

Combining everything

Real chemistry mixes every construct:

Source Rendered

^14C_6H_12O_6 + 6O_2 -> 6CO_2 + 6H_2O `Delta G = -2870 kJ/mol`

${{}^{14}\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6+6{\mathrm{O}}_2\to 6\mathrm{C}{\mathrm{O}}_2+6{\mathrm{H}}_2\mathrm{O}{\displaystyle \Delta G=-2870k\frac{J}{m}ol}$

A radioactive glucose combustion with embedded thermodynamics.

Canonicalisation rules

Construct	Input	Output	Rule
Charge	Ca^+2	Ca^2+	IUPAC number-then-sign
Everything else	—	unchanged	The formatter only normalises marker spellings

Quick lookup by use case

Writing a formula

Elements + subscripts: H_2SO_4, C_6H_12O_6

Writing an ion

Element + charge: Na^+, SO_4^2-

Writing an isotope

Prefix isotope: ^14C, ^131I

Writing a reaction

Reactants -> products: 2H_2 + O_2 -> 2H_2O

Writing equilibrium

Use <=> with conditions: N_2 + 3H_2 <=>[Fe][400C] 2NH_3

Writing a bond

Between atoms: H-O-H, HC#CH, H_2C=CH_2

Writing a group

Parenthesised: Ca(OH)_2, (NH_4)_2SO_4

Writing math

Backtick-wrapped: `K_a = [H+][A-]/[HA]`