Beginner perfumer #112: the aldehyde C-number stops being a carbon count at C-12

About a 5 minute read.

The short version

• The corpus holds 501 records written in aldehyde C-numbering, across 28 spellings
• C-6 through C-12 are honest: the number is the carbon count and the material is an aldehyde
• C-14, C-16 and C-18 are none of those things

Number	What it actually is	Formula	Carbons
C-14	gamma-undecalactone	C11H20O2	11
C-16	ethyl methylphenylglycidate	C12H14O3	12
C-18	gamma-nonalactone	C9H16O2	9

• The database appends (so-called) to all three names itself
• Across eight name pairs, no formula ever uses both spellings; every overlap is zero
• After merging, gamma-undecalactone moves from 29th to 15th

The biggest block the last article left

Last round I measured which name normalisation pays and pushed coverage from 60.32% to 72.81%. Of the 4,753 records still unmatched, the largest single type is the aldehyde C-numbering, and I said then that no string normalisation would reach it. Something else was hiding in the unmatched records: 14 molecular weight fields hold a mass that counts only the carbons.

aldehyde c-14 and gamma-undecalactone share not one character.

What the numbering is

An early twentieth-century trade convention. Fatty aldehydes were sold numbered by carbon count: C-8 is octanal, C-10 is decanal, C-12 is dodecanal. Simple, memorable, and it spares you the chemical names.

The corpus still uses it, in 501 records across 28 spellings: aldehyde c-10, aldehyde c 10, aldehyde c-10 10% dpg, aldehyde c 10 decylic, and so on.

The lookup table

I resolved each number back to the database and pulled its formula and carbon count:

Number	Database material	Formula	Carbons	Match	Suppliers
C-6	hexanal	C6H12O	6	✓	70
C-7	heptanal	C7H14O	7	✓	41
C-8	octanal	C8H16O	8	✓	73
C-9	nonanal	C9H18O	9	✓	63
C-10	decanal	C10H20O	10	✓	92
C-11 undecylenic	10-undecenal	C11H20O	11	✓	41
C-11 undecylic	undecanal	C11H22O	11	✓	35
C-11 MOA	2-methyl decanal	C11H22O	11	✓	18
C-11 intreleven	intreleven aldehyde	C11H20O	11	✓	21
C-12 lauric	dodecanal	C12H24O	12	✓	53
C-12 MNA	2-methyl undecanal	C12H24O	12	✓	40
C-14	gamma-undecalactone	C11H20O2	11	✗ a lactone	119
C-16	strawberry glycidate	C12H14O3	12	✗ an epoxy ester	63
C-18	gamma-nonalactone	C9H16O2	9	✗ a lactone	96

In those eleven rows from C-6 to C-12, every number is the carbon count and every material is an aldehyde. Within that range the system works exactly as advertised.

Then it breaks.

The database knows

I expected to have to work this out myself. Opening the records, the name field reads:

gamma-undecalactone (aldehyde C-14 (so-called))
strawberry glycidate 1 (aldehyde C-16 (so-called))
gamma-nonalactone (aldehyde C-18 (so-called))

(so-called). The database disowns the name inside the name field.

None of the other eleven carry that marker. decanal (aldehyde C-10), octanal (aldehyde C-8) and dodecanal (aldehyde C-12 lauric) are all written straight, with no annotation.

Whoever compiled this knew which three were lies and flagged them. It is the most candid piece of self-annotation I have found in this database.

The one with the most suppliers is the least honest

C-14 (gamma-undecalactone) has 119 suppliers, more than any genuine aldehyde in the table. C-18 has 96, C-16 has 63.

Of the three most popular members of the "aldehyde C series", two are lactones and one is an epoxy ester.

C-12 covers two different materials

Even inside the honest range, the number alone is not enough:

	C-12 lauric	C-12 MNA
Material	dodecanal (straight chain)	2-methyl undecanal (branched)
Formula	C12H24O	C12H24O
Vapour pressure @25 °C	0.034	1.428
Suppliers	53	40

Same molecular formula, different molecules, with a 42-fold difference in vapour pressure. A formula that just says aldehyde c-12 — and one in the corpus does — leaves you unable to tell.

Incidentally, the substantivity field jumps 39-fold between C-8 and C-9

Building the table I pulled substantivity along with everything else:

Number	Vapour pressure	Substantivity
C-6	10.888	4 h
C-7	3.854	12 h
C-8	2.068	7 h
C-9	0.532	276 h
C-10	0.207	224 h

One carbon takes 7 hours to 276. The vapour pressures differ by 3.9-fold, and at the roughly 5.85x per decade I computed, 3.9-fold should buy about 2.6x, or around 18 hours.

And C-12 MNA's vapour pressure of 1.428 is barely below octanal's 2.068, yet it reads 388 hours.

I already wrote that this field should be read as a ranking. Here is another set of evidence.

No formula uses both spellings

Before merging I checked one thing: if aldehyde c-14 and gamma-undecalactone really are the same material, no formula should list both, since that would be writing one material down twice.

All eight pairs:

C-number spelling	Formulas	Chemical-name spelling	Formulas	Both
aldehyde c-14	64	gamma-undecalactone	85	0
aldehyde c-10	64	decanal	21	0
aldehyde c-12 lauric	51	dodecanal	20	0
aldehyde c-18	25	gamma-nonalactone	17	0
aldehyde c-9	25	nonanal	9	0
aldehyde c-8	27	octanal	7	0

Zero throughout. Each formula's author picks one convention and uses it start to finish. That both supports the identification and means merging will not double-count.

Merging moves everything up

Material	Before: formulas / rank	After: formulas / rank
gamma-undecalactone	85 / 29th	149 / 15th
decanal	64 / 44th	103 / 25th
dodecanal	51 / 65th	83 / 32nd
10-undecenal	59 / 51st	77 / 37th
2-methyl undecanal	60 / 49th	67 / 42nd
gamma-nonalactone	25 / 135th	42 / 78th
nonanal	25 / 134th	42 / 78th
octanal	27 / 119th	38 / 85th

Gamma-undecalactone lands at 15th across 954 formulas, one of the most-used materials in the corpus, having previously been split in half and looking like two mid-table materials.

The rule you can copy

In code, this table is a dict:

c-6 → hexanal            c-11 undecylenic → 10-undecenal
c-7 → heptanal           c-11 undecylic   → undecanal
c-8 → octanal            c-11 moa         → 2-methyl decanal
c-9 → nonanal            c-12 lauric      → dodecanal
c-10 → decanal           c-12 mna         → 2-methyl undecanal
c-14 → gamma-undecalactone
c-16 → ethyl methylphenylglycidate
c-18 → gamma-nonalactone

Collapse the 28 spellings into one with re.sub(r'ald(ehyde)?\s*c[-\s]*', 'c-', name) first, then look it up.

What this doesn't establish

• I do not know why C-14, C-16 and C-18 carry those numbers. The common explanation is that their odours were classified as equivalent to an aldehyde of that carbon count, but I could not find a primary source to cite, so I am not writing it.
• The table covers only the numbers the corpus uses. I did not look at C-13, C-15, C-17 or C-20; they do not appear here.
• "No formula uses both" is a necessary condition, not a sufficient one. It is consistent with the two being the same material but does not prove it alone. The real evidence is the database's own name field putting both names together.
• The merged ranks are ranks within these 954 formulas, not market share.
• I did not handle aldehyde c-11 intreleven or undecenal mixture. Neither appears in the corpus, but both are in the database, and the first shares 10-undecenal's vapour pressure and substantivity exactly (0.039 and 380 hours), so it may be a duplicate record. I did not check.
• Mason and colleagues titled their 1978 toxicology study with "strawberry aldehyde" (PMID 711053). Even the toxicology literature uses the wrong name. The problem does not start with this database.