Question: What is the shorthand notation for the carboxylic acid in the most common type of sunflower seed?

Context paragraphs:
Uronic acid: Uronic acids ( ) are a class of sugar acids with both carbonyl and carboxylic acid functional groups.  They are sugars in which the terminal carbon's hydroxyl group has been oxidized to a carboxylic acid.  Oxidation of the terminal aldehyde instead yields an aldonic acid, while oxidation of both the terminal hydroxyl group and the aldehyde yields an aldaric acid.  The names of uronic acids are generally based on their parent sugars, for example, the uronic acid analog of glucose is glucuronic acid.  Uronic acids derived from hexoses are known as hexuronic acids and uronic acids derived from pentoses are known as penturonic acids.

Ketonic decarboxylation: Ketonic decarboxylation (also known as ketonization) is a type of organic reaction and a decarboxylation converting two equivalents of a carboxylic acid to a symmetric ketone by the application of heat with expulsion of one equivalent of water and one equivalent of carbon dioxide.  Bases promote this reaction.  The reaction mechanism likely involves nucleophilic attack of the alpha-carbon of one acid group on the other acid group's carbonyl, possibly as a concerted reaction with the decarboxylation.  The initial formation of an intermediate carbanion with decarboxylation from one acid group prior to the nucleophilic attack has been proposed, but is unlikely since the byproduct resulting from the carbanion's protonation by the acid has never been reported.  This reaction is different from oxidative decarboxylation, which proceeds through a radical mechanism and is characterised by a different product distribution in isotopic labeling experiments with two different carboxylic acids.  With two different carboxylic acids, the reaction behaves poorly because of poor selectivity except when one of the acids (for example, a small, volatile one) is used in large excess.

Carboxylic acid: A carboxylic acid is an organic compound that contains a carboxyl group (C(=O)OH).  The general formula of a carboxylic acid is R–COOH, with R referring to the rest of the (possibly quite large) molecule.  Carboxylic acids occur widely and include the amino acids (which make up proteins) and acetic acid (which is part of vinegar and occurs in metabolism).

Stickland fermentation: Stickland fermentation or The Stickland Reaction is the name for a chemical reaction that involves the coupled oxidation and reduction of amino acids to organic acids.  The electron donor amino acid is oxidised to a volatile carboxylic acid one carbon atom shorter than the original amino acid.  For example, alanine with a three carbon chain is converted to acetate with two carbons.  The electron acceptor amino acid is reduced to a volatile carboxylic acid the same length as the original amino acid.  For example, glycine with two carbons is converted to acetate.

Sunflower seed: The sunflower seed is the fruit of the sunflower ("Helianthus annuus").  There are three types of commonly used sunflower seeds: linoleic (most common), high oleic, and NuSun developed for sunflower oil.  Each variety has its own unique levels of monounsaturated, saturated, and polyunsaturated fats.  The information in this article refers mainly to the linoleic variety.

D-Galacturonic acid: D-Galacturonic acid is a sugar acid, an oxidized form of -galactose.  It is the main component of pectin, in which it exists as the polymer polygalacturonic acid.  In its open form, it has an aldehyde group at C1 and a carboxylic acid group at C6.  Other oxidized forms of -galactose are -galactonic acid (carboxylic group at C1) and "meso"-galactaric acid (mucic acid) (carboxylic groups at C1 and C6).  It is also a uronic acid or hexuronic acid.  Naturally occurring uronic acids are -glucuronic acid, -galacturonic acid, -iduronic acid and -mannuronic acid.

Linoleic acid: Linoleic acid (LA), a carboxylic acid, is a polyunsaturated omega-6 fatty acid, an 18-carbon chain with two double bonds in cis configuration.  A shorthand notation like "18:2 (n-6)" or "18:2 "cis"-9,12" may be used in literature.  It occurs in nature as a triglyceride ester, free fatty acids are typically low in foods.

Arndt–Eistert reaction: The Arndt–Eistert synthesis is a series of chemical reactions designed to convert a carboxylic acid to a higher carboxylic acid homologue (i.e. contains one additional carbon atom) and is considered a homologation process.  Named for the German chemists Fritz Arndt (1885–1969) and Bernd Eistert (1902–1978), Arndt–Eistert synthesis is a popular method of producing β-amino acids from α-amino acids.  Acid chlorides react with diazomethane to give diazoketones.  In the presence of a nucleophile (water) and a metal catalyst (AgO), diazoketones will form the desired acid homologue.

Barton decarboxylation: The Barton decarboxylation is a radical reaction in which a carboxylic acid is first converted to a thiohydroxamate ester (commonly referred to as a Barton ester).  The product is then heated in the presence of a radical initiator and a suitable hydrogen donor to complete the reductive decarboxylation of the initial carboxylic acid.  Using this reaction it is possible to remove a carboxylic acid moiety from an alkyl group and replace it with other functional groups.  (See Scheme 1) This reaction is named after its developer, the British chemist and Nobel laureate Sir Derek Barton (1918–1998).

Organic acid anhydride: An organic acid anhydride is an acid anhydride that is an organic compound.  An acid anhydride is a compound that has two acyl groups bonded to the same oxygen atom.  A common type of organic acid anhydride is a carboxylic anhydride, where the parent acid is a carboxylic acid, the formula of the anhydride being (RC(O))O. Symmetrical acid anhydrides of this type are named by replacing the word "acid" in the name of the parent carboxylic acid by the word "anhydride".  Thus, (CHCO)O is called "acetic anhydride."  Mixed (or unsymmetrical) acid anhydrides, such as acetic formic anhydride (see below), are known.

Supporting paragraphs: Sunflower seed Linoleic acid
Answer: "18:2 (n-6)" or "18:2 "cis"-9,12"