12
$\begingroup$

My understanding is that we should avoid MathJax in titles because it breaks searching and indexing of questions. andselisk recently told me to avoid using $\beta$ in "β-keto ester." That seems like a reasonable request to me since MathJax seems overkill for one character. Also, symbols like Å or ⦵ have no simple representation using MathJax.

I'm happy to comply with these recommendations, but the reason I am using MathJax is that it's easy to remember and enter. What are good ways to input other Unicode characters in titles or for one-off characters in text?

$\endgroup$
0
7
$\begingroup$

This is a supplementary post to gather together the most commonly used symbols on Chemistry.SE and the compose key sequences for a Windows user running WinCompose. The following list includes a symbol, keyboard sequence (compose key is normally the Right Alt button), Unicode character and description, as well as examples on the next line:

⎄ Compose - - = U+2212 MINUS SIGN
−42;
C−C bond (when not using mhchem, esp. in conjunction with double bond C=C).

⎄ Compose - - . U+2013 EN DASH
acid–base titration;
acetonitrile–water mixture;
Ziegler–Natta catalyst;
1–2 kg.

⎄ Compose - - - U+2014 EM DASH
"All three experimental parameters—temperature, time, and concentration—were strictly followed."

⎄ Compose = = U+2261 IDENTICAL TO
a ≡ b (also: $a ≡ b$ ($a ≡ b$));
C≡C bond.

⎄ Compose ~ = U+2245 APPROXIMATELY EQUAL TO
A ≅ B.

⎄ Compose ~ ~ U+2248 ALMOST EQUAL TO
e ≈ 2.72.

⎄ Compose / = U+2260 NOT EQUAL TO
MathJax ≠ $\mathrm\LaTeX$.

⎄ Compose < = U+2264 LESS-THAN OR EQUAL TO
x ≤ y (also: $x ≤ y$ ($x ≤ y$)).

⎄ Compose > = U+2265 GREATER-THAN OR EQUAL TO
x ≥ y (also: $x ≥ y$ ($x ≥ y$)).

⎄ Compose + < U+226A MUCH LESS-THAN
x ≪ y (also: $x ≪ y$ ($x ≪ y$)).

⎄ Compose + > U+226B MUCH GREATER-THAN
x ≫ y (also: $x ≫ y$ ($x ≫ y$)).

± ⎄ Compose + - U+00B1 PLUS-MINUS SIGN
(142 ± 13) pm (also: $\pu{(142 ± 13) pm}$ ($\pu{(142 ± 13) pm}$)).

· ⎄ Compose . - U+00B7 MIDDLE DOT
BF3 · THF (also: $\ce{BF3·THF}$ ($\ce{BF3·THF}$));
HO· radical;
n = c · V (also: $n = c · V$ ($n = c · V$));
3 · 106 m/s (also: $\pu{3e6 m/s}$ ($\pu{3e6 m/s}$)).

⎄ Compose * 1 U+2022 BULLET
HCO•+ radical (useful when superscripted for denoting a radical, esp. in conjunction with plus/minus (e.g. <sup>•+</sup>)).

× ⎄ Compose x x U+00D7 MULTIPLICATION SIGN
1.2 × 3 = 3.6 (also: $1.2 × 3 = 3.6$ ($1.2 × 3 = 3.6$));
6.022 × 1023 mol−1 (also: $\pu{6.022E23 mol-1}$ ($\pu{6.022E23 mol-1}$)).

° ⎄ Compose o o U+00B0 DEGREE SIGN
57.296° (also: $57.296°$ ($57.296°$));
298.15 °C (also: $\pu{298.15 °C}$ ($\pu{298.15 °C}$))

⎄ Compose . . U+2026 HORIZONTAL ELLIPSIS
1, 2, 3, ….

Å ⎄ Compose o A U+00C5 LATIN CAPITAL LETTER A WITH RING ABOVE (aka angstrom symbol)
Bond length is 1.23 Å.

à ⎄ Compose ~ A U+00C3 LATIN CAPITAL LETTER A WITH TILDE
Electronic state of polyatomic molecule Ã.

â ⎄ Compose ^ a U+00E2 LATIN SMALL LETTER A WITH CIRCUMFLEX
Le Châtelier's principle.

à ⎄ Compose ` a U+00E0 LATIN SMALL LETTER A WITH GRAVE
vis-à-vis.

ä ⎄ Compose " a U+00E4 LATIN SMALL LETTER A WITH DIAERESIS
Friedländer quinoline synthesis.

é ⎄ Compose ' e U+00E9 LATIN SMALL LETTER E WITH ACUTE
déjà vu

ö ⎄ Compose " o U+00F6 LATIN SMALL LETTER O WITH DIAERESIS
Wöhler Synthesis of urea.

ß ⎄ Compose s s U+00DF LATIN SMALL LETTER SHARP S
Mößbauer spectroscopy

ü ⎄ Compose " u U+00FC LATIN SMALL LETTER U WITH DIAERESIS
Büchner flask.

é ⎄ Compose ' e U+00E9 LATIN SMALL LETTER E WITH ACUTE
Kekulé

ø ⎄ Compose / o U+00F8 LATIN SMALL LETTER O WITH STROKE
Brønsted–Lowry theory.

⎄ Compose d ` U+1D05 LATIN LETTER SMALL CAPITAL D
ᴅ-phenylglycine.

ʟ ⎄ Compose l ` U+029F LATIN LETTER SMALL CAPITAL L
ʟ-lactic acid.

α ⎄ Compose * a U+03B1 GREEK SMALL LETTER ALPHA
α-helix.

β ⎄ Compose * b U+03B2 GREEK SMALL LETTER BETA
β-decay.

γ ⎄ Compose * g U+03B3 GREEK SMALL LETTER GAMMA
γ-hydroxybutyric acid.

δ ⎄ Compose * d U+03B4 GREEK SMALL LETTER DELTA
δ– charge.

Δ ⎄ Compose * D U+0394 GREEK CAPITAL LETTER DELTA
Δ-ruthenium-tris(bipyridine).

ε ⎄ Compose * e U+03B5 GREEK SMALL LETTER EPSILON
ε is the molar absorptivity.

ζ ⎄ Compose * z U+03B6 GREEK SMALL LETTER ZETA
ζ-potential.

θ ⎄ Compose * u U+03B8 GREEK SMALL LETTER THETA
θ is the angle of scattering.

κ ⎄ Compose * k U+03BA GREEK SMALL LETTER KAPPA
κ6-EDTA.

λ ⎄ Compose * l U+03BB GREEK SMALL LETTER LAMDA
wavelength λ.

Λ ⎄ Compose * L U+039B GREEK CAPITAL LETTER LAMDA
molar conductivity Λ.

μ ⎄ Compose * m U+03BC GREEK SMALL LETTER MU
4.2 μmol.

ν ⎄ Compose * n U+03BD GREEK SMALL LETTER NU
ν = c/λ.

ξ ⎄ Compose * j U+03BE GREEK SMALL LETTER XI
ξ is the extent of reaction.

π ⎄ Compose * p U+03C0 GREEK SMALL LETTER PI
π-electron.

ρ ⎄ Compose * r U+03C1 GREEK SMALL LETTER RHO
ρ is the density.

σ ⎄ Compose * s U+03C3 GREEK SMALL LETTER SIGMA
σ bond.

τ ⎄ Compose * t U+03C4 GREEK SMALL LETTER TAU
bent bond τ.

φ ⎄ Compose * f U+03C6 GREEK SMALL LETTER PHI
φ bond.

χ ⎄ Compose * x U+03C7 GREEK SMALL LETTER CHI
χ is the electronegativity.

ψ ⎄ Compose * c U+03C8 GREEK SMALL LETTER PSI
ψ is the wave function.

ω ⎄ Compose * v U+03C9 GREEK SMALL LETTER OMEGA
ω is the mass fraction.

⎄ Compose d a g U+2020 DAGGER
Footnote†.

⎄ Compose d d a g U+2021 DOUBLE DAGGER
Footnote‡;
denotes a [transition state]‡.

⎄ Compose U+2192 RIGHTWARDS ARROW
A + B → C + D.

ʹ ⎄ Compose * ' U+02B9 MODIFIER LETTER PRIME
2,2′-bipyridine.

⎄ Compose * . " U+2033 DOUBLE PRIME
47°8′23″;
hν = E′ − E″ (also: $hν = E′ − E″$ ($hν = E′ − E″$)).

⎄ Compose @ < U+276C MEDIUM LEFT-POINTING ANGLE BRACKET ORNAMENT
⎄ Compose @ < U+276D MEDIUM RIGHT-POINTING ANGLE BRACKET ORNAMENT
❬+|−❭ (bra–ket notation);
❬x❭ (average/mean value).

⎄ Compose 6 ' U+2018 LEFT SINGLE QUOTATION MARK
⎄ Compose 9 ' U+2019 RIGHT SINGLE QUOTATION MARK
‘high-6 high-9’ (British English).

⎄ Compose 6 " U+201C LEFT DOUBLE QUOTATION MARK
⎄ Compose 9 " U+201D RIGHT DOUBLE QUOTATION MARK MARK
“high-66 high-99” (American English).

⎄ Compose , " U+201E DOUBLE LOW-9 QUOTATION MARK
⎄ Compose 6 " U+201C LEFT DOUBLE QUOTATION MARK
„low-99 high-66“ (German).

« ⎄ Compose < < U+00AB LEFT-POINTING DOUBLE ANGLE QUOTATION MARK MARK
» ⎄ Compose > > U+00BB RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK
«guillemets» (French, Russian, Swiss German).

₀₁₂₃₄₅₆₇₈₉ ⎄ Compose _ <number 0–9> lowercase number 0–9 (also works with some other characters)
H₂O.

⁰¹²³⁴⁵⁶⁷⁸⁹ ⎄ Compose ^ <number 0–9> uppercase number 0–9 (also works with some other characters)
Cr³⁺.

(ノಥ益ಥ)ノ彡┻━┻ ⎄ Compose t f Table flip like a boss (not an actual Unicode symbol; can be found in chat)
— "hI... plz asap wat is number of moles in 18G h20?!, thx bai"
— *question becomes HNQ*
— (ノಥ益ಥ)ノ彡┻━┻

The majority of these combination will also work for Linux users out of the box. One can also search for the key combinations in the dialogue opening via double-clicking on the tray icon wincompose tray icon.

Keep in mind: if you lack a combination for a symbol, you can always create/edit ~/.XCompose file. I always append some commands to mine:

<Multi_key> <minus> <0> <minus>: "⦵"  U29B5  # PLIMSOLL
<Multi_key> <a> <n> <g> <l> <e>: "∠"  U2220  # ANGLE
<Multi_key> <e> <q> : "⇌"  U21CC  # RIGHTWARDS HARPOON OVER LEFTWARDS HARPOON

which allow me to type in the following way:

⎄ Compose - 0 - U+29B5 CIRCLE WITH HORIZONTAL BAR
$Δ_\mathrm fH^⦵$ ($Δ_\mathrm fH^⦵$).

⎄ Compose a n g l e U+2220 ANGLE
∠H−O−H ≅ 104.5°.

⎄ Compose e q U+21CC RIGHTWARDS HARPOON OVER LEFTWARDS HARPOON
2 H₂O ⇌ H₃O⁺ + OH⁻

Windows users can right-click on WinCompose tray icon wincompose tray icon, select Options…CompositingSequences and click Edit button next to user-defined sequences:

editing ~/.XCompose

$\endgroup$
4
  • 2
    $\begingroup$ Wow, this is a lot of very helpful information! Even though I mostly use a Mac, thanks for making this available! $\endgroup$
    – Ed V
    Jun 20 '20 at 12:56
  • $\begingroup$ Is C–C bond supposed to be minus sign? I've always been using en dash, which the (old) ACS Style Guide recommends for prose ("carbon–oxygen bond") i.stack.imgur.com/sHUhc.png, although it doesn't say anything about when using element symbols $\endgroup$
    – orthocresol Mod
    Jun 20 '20 at 16:52
  • 2
    $\begingroup$ Hmm, the minus sign is better aligned when put alongside an equals sign... en dash C–C=C and minus sign C−C=C Seems to depend on the font though. $\endgroup$
    – orthocresol Mod
    Jun 20 '20 at 16:53
  • $\begingroup$ @orthocresol Exactly, and kerning of minus sign is also more consistent with double and triple bonds too: C−C=C≡C (minus) vs. C–C=C≡C (en dash). (Especially when copied to a text editor and enlarged 800%:) ) $\endgroup$
    – andselisk Mod
    Jun 20 '20 at 17:00
6
$\begingroup$

One solution, which I use at work on my Linux workstation, is to use a Compose key. Unfortunately, my home workstation uses a standard 101-key keyboard and does not have a compose key.

However, there are plenty of apps that allow you to remap a key as compose. For example, WinCompose. See also this post on Super User.

$\endgroup$
5
$\begingroup$

For macOS, Cmd-Ctrl-Space brings up a Character Viewer screen where you can search for the appropriate symbol using its Unicode name. For example, to type α (U+03B1 Greek Small Letter Alpha):

$\endgroup$
3
$\begingroup$

You can write Greek letters and most other special characters using HTML character entities. For example, typing:

&alpha; &beta; &gamma; &delta; &epsilon;

in the edit box will produce the output "α β γ δ ε". For capital Greek letters, just capitalize the first letter of the name: e.g. &Delta; produces "Δ".

The Ångström sign Å can be obtained with &Aring; (if you don't happen to have a keyboard that has a key for it, like I do), and the Plimsoll sign ⦵ can be obtained with &ohbar;. Some other potentially useful named character entities include ≤ (&le;), ≥ (&ge;), ≈ (&approx;), ° (&deg;) and the various arrow symbols like ← (&larr;), → (&rarr;), ↔ (&harr;) and ⇌ (&rlhar; or &Equilibrium;). For more examples, here's a handy list on named HTML character entities by the W3C.

Conveniently, quite many of these HTML entity names match the corresponding LaTeX / MathJax commands for the same symbols, although that's not always the case.

I don't think HTML entities work in the question title (and they definitely don't work in comments) but, as a work-around, you can always type the entity into the edit box for the question body and then copy-paste the actual character from the preview area into the title.


Not all Unicode characters have named character entities, but if you know their Unicode code point, you can still write them using a numeric character entity of the form &#1234; or &#xABCD;, where 1234 and ABCD stand for the decimal and the hexadecimal number of the character in Unicode. For example, should you for some reason need the biohazard sign (U+2623) ☣︎, you can get it by typing &#x2623; into the edit box.

(Note that some browsers may render the biohazard sign I used as an example above as an emoji. In theory, you should be able to select the non-emoji variant by adding the invisible variation selector character &#xFE0E; immediately after it. In practice that doesn't always work, e.g. if the reader's browser has chosen to use a font that only has the emoji variant available.)

You can usually find the code points for various characters by searching for the on Google or looking them up on various Unicode reference sites like the fileformat.info site I linked to above. Then again, if you've gone to that much trouble, you usually might as well just copy-paste the character from the site.


Ps. If you do want to use MathJax but need a Unicode symbol that has no corresponding LaTeX command, you can also use the \unicode command to enter it using its Unicode code point. For example, $\unicode{x2623}$ gives the biohazard sign $\unicode{x2623}$.

Unfortunately I'm not aware of any way to use named HTML character entities directly in MathJax, unless a matching MathJax / LaTeX command just happens to exist. So, for example, $\Delta$ will indeed produce a $\Delta$ in MathJax too, but $\ohbar$ just gives $\ohbar$.

One solution, if you do remember the HTML character entity name, is to use the same work-around as I suggested above for titles, i.e. to type the HTML entity into the edit box (without dollar signs) and then copy-paste the actual character from the preview panel into the MathJax code.

$\endgroup$
6
  • 1
    $\begingroup$ The main disadvantage of HTML entities is they work exclusively inside {X|HT}ML documents and also heavily rely on browser and web page settings. Compose key, on the other hand, is more robust: it works system-wide (app-agnostic) with the guaranteed result provided the loaded font includes the required glyph. You remember a key sequence once and use it everywhere, not just in your browser. $\endgroup$
    – andselisk Mod
    Jun 28 '20 at 8:35
  • $\begingroup$ And the main advantage of HTML is that they are system independent: if &alpha; works on a website from my home Linux system it will work on the same website at work using Windows or on the off-chance that I get to deal with iOS again. $\endgroup$
    – Jan
    Jun 29 '20 at 9:14
  • $\begingroup$ @Jan …and so do the Unicode symbols entered with the compose key, whose combinations are likely identical or very similar across all systems since the concept stems from Xorg project. And good luck using HTML entities for actual work using either office apps or LaTeX. $\endgroup$
    – andselisk Mod
    Jun 29 '20 at 12:47
  • $\begingroup$ @andselisk For the sake of the argument: Compose key requires me installing software; I may or may not have the permission to do that on the system I happen to be on. For office or TeX, I do have to remember a different set of commands – but since I memorize the &/\ along with the command following it, that’s a different set of memorised items in my brain. $\endgroup$
    – Jan
    Jun 29 '20 at 14:00
  • $\begingroup$ @Jan Compose key works out of the box on most Linux distros and on Windows WinCompose doesn't require administrative permissions and can also run in portable mode, so technically there is no installation needed anywhere. Thanks to XeLaTeX and fonts like STIX2/XITS (Serif) and Noto/Lato (Sans), there is also no need for TeX users to remember different macros for inputting characters. As for the office apps, that's precisely where compose key shines as there is only limited support for custom autocorrect macros and highly unintuitive numeral Unicode sequences. $\endgroup$
    – andselisk Mod
    Jun 29 '20 at 14:13
  • $\begingroup$ @Jan …and what about your terminal, messenger or a search field in PDF viewer or web browser? They won't ever interpret a \AA or &Aring; correctly (well, maybe a terminal after some tweaking will), but Meta+o+A will work everywhere all the time giving "Å". It seems to me that the compose key is exactly what you meant by reducing a set of memorized items. $\endgroup$
    – andselisk Mod
    Jun 29 '20 at 14:17
2
$\begingroup$

Try http://shapecatcher.com/ - simply draw a shape and press "Recognize". It will attempt to convert the drawing to Unicode. ShapeCatcher usually offers many suggestions, some good and some poor, which you can vote on. It's convenient if you don't know the name.

It's the Unicode version of Detextify except it waits for you to indicate that you have finished drawing, and it offers better and more suggestions.

ShapeCatcher Examples:

  • Angstrom sign: Å - Unicode hexadecimal: 0x212b

  • Latin capital letter a with ring above: Å - Unicode hexadecimal: 0xc5

A suggestion that seems good may not be the best. In some cases exact rendering can depend on the fonts available, a problem which MathJax solves. Because the angstrom is named after Anders Jonas Ångström the symbol is actually a letter in the Swedish language alphabet, and a few others, it's correct to use an a-ring character.

Another method is: https://www.toptal.com/designers/htmlarrows/math/ and http://www.amp-what.com/ - if you know the name of the Unicode character.

Results Comparison:

MathJax ShapeCatcher Toptal Amp-What
$\overset{\lower.5em\circ}{\mathrm{A}}$ Å &0xC5; &#x212B; &#8491; or Å &#197; or &Aring;
$\mathbb {F}$ 𝔽 &#x1D53D; No Suggestion 𝔽 &#120125; or &Fopf;
$\aleph_0$ No Suggestion No Suggestion &#67648; + &#8320;

In some cases finding a substitute can be a nightmare.

If you are concerned about searching then having several ways to write the same thing doesn't improve that situation, but if it's only a few characters (and the answers both don't require MathJax and use Unicode) then using Unicode-only makes the webpage load a fraction of a second quicker, and preserves the appearance in the HNQ List on non-MathJax sites.

See also: Math.meta.SE FAQ- "Guidelines for good use of MathJax in question titles"

$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .