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Sci.chem FAQ - Part 3 of 7
Section - 12. Nomenclature

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12.1  What are CAS Registry Numbers?

When chemicals are first encountered by the Chemical Abstracts Service, they
are assigned a unique number when they are registered. These numbers are not
related to any structure or property of the molecule, they are arbitrarily
assigned. It should be remembered that occasionally a compound may be 
accidentally assigned two or more numbers - especially industrial products
that have not been completely characterised. When this is discovered, one of
the numbers is no longer used. The numbers usually take the form of
[xx-yy-z to xxxxxx-yy-z] and square brackets are often used in monographs to
identify the CAS Registry Number [RN]. The easiest way to locate the CAS RN 
for commercially-available chemicals is to look in suppliers catalogues 
( eg Aldrich) or compilations ( eg Merck or Hawley ), almost all chemical
texts now list the RN, and several ( eg Merck Index and Aldrich ) have a 
cross-reference Index. The RN is extremely useful for on-line searching of 
Chemical Abstracts and several other popular chemistry-related databases, 
but is not particularly useful for the hardcopy version, except to confirm 
compound identity.

12.2  What are the correct names of recently-discovered elements? 
     
The Transfermium Working Group was established in 1986 by the International 
Union of Pure and Applied Chemistry (IUPAC) and the International Union of 
Pure and Applied Physics (IUPAP). The working  group published several 
reports, and then recommended that elements should not be named after living 
persons [1]. This greatly upset the USA - who wanted to name an element after 
G. Seaborg. After protracted negotiations, a compromise selection of names  
was finally approved by the IUPAC Commission on Nomenclature in Inorganic
Chemistry, the IUPAC Inorganic Division, the IUPAC Bureau, and the selection 
was eventually ratified by the IUPAC Council meeting in Geneva during August 
1997 [2].

101      Mendelevium    Md             D. Mendeleev (Russia)
102      Nobelium       No             Nobel Institute (Sweden)
103      Lawrencium     Lr             E. Lawrence (USA) 
104      Rutherfordium  Rf             E. Rutherford (NZ)
105      Dubnium        Db             Dubna = Russian Research Centre
106      Seaborgium     Sg             G. Seaborg (USA)
107      Bohrium        Bh             N. Bohr (Denmark)
108      Hassium        Hs             Latin name for German state of Hesse
109      Meitnerium     Mt             L. Meitner (Austria) 
 
Note that Hesse is where the German heavy-element laboratory is based. 
The Gesellschaft fur Schwerionenforschung (GSI) was responsible for the
first man-made creation of elements 107-110. The compromise will now move
attention to the naming the recently-discovered elements 110-112.

12.3  What is the nomenclature system for CFCs/HCFCs/HFCs?

The CFC naming system was developed by T.Midgley,Jr. and A.L.Henne in 1929, 
and further refined by J.D.Park. Originally, organic molecules that contained
Chlorine and Fluorine were all referred to as CFCs. Today, the group is
subdivided into CFCs, HCFCs, and HFCs. The naming system consists of:-

CFC-01234a  where 0 = number of double bonds ( omitted if zero )
                  1 = Carbon atoms - 1 ( omitted if 0 )
                  2 = Hydrogen atoms + 1
                  3 = Fluorine atoms
                  4 = Chlorine atoms replaced by Bromine ("B" prefix added )
                  a = letter added to identify isomers, the "normal" isomer 
                     in any number has the smallest mass difference on each
                     carbon, and a, b, or c are added as the masses diverge 
                     from normal.

If the compound is cyclic, then the number is prefixed with "C". There are 
several other refrigerants, some of which are hydrocarbons, hydrocarbon 
blends, or CFC blends. Full details of the nomenclature system are specified 
in ANSI/ASHRAE Standard 34-1992 with additional annual supplements. Chemical 
names are frequently used in place of the numbers for common materials 
- such as trichloroethylene and chloroform. The specified ANSI/ASHRAE 
prefixes were FC ( FluoroCarbon ), or R ( Refrigerant ), but today most are 
prefixed by more specific classifications - such as CFC, HCFC, and HFC.  

CFC-11     CCl3F        trichlorofluoromethane                   [75-69-4]
CFC-12     CCl2F2       dichlorodifluoromethane                  [75-71-8]
CFC-113    CCl2F-CClF2  1,1,2-trichlorotrifluoroethane           [76-13-1]
HCFC-22    CHClF2       chlorodifluoromethane                    [75-45-6]
HCFC-123   CHCl2-CF3    2,2-dichloro-1,1,1-trifluoroethane       [306-83-2] 
HCFC-123a  CHClF-CClF2  1,2-dichloro-1,1,2-trifluoroethane       [354-23-4] 
HFC-23     CHF3         trifluoromethane                         [75-46-7]
HFC-134    CHF2-CHF2    1,1,2,2-tetrafluoroethane                [359-35-3]    
HFC-134a   CH2F-CF3     1,2,2,2-tetrafluoroethane                [811-97-2]
R-20       CHCl3        chloroform                               [67-66-3]
R-22B1     CHBrF2       bromodifluoromethane                     [1511-62-2]
R-1120     CHCl=CCl2    trichloroethylene                        [79-01-6]
R-1150     CH2=CH2	ethylene                                 [74-85-1]
R-C316     C4Cl2F6      1,2-dichlorohexafluorocyclobutane

Another technique for naming CFCs uses the addition of 90 to the CFC number
to produce a "def" number which corresponds to the CHF composition. If
(e + f) < (2d + 2), then additional atoms are required for saturation. This
technique has been described in detail in the Journal of Chemical Education 
[3].

ASHRAE     +90     Empirical Composition    Formula     
                   C  H  F   (+Cl)
CFC-11     101     1  -  1     3            CCl3F
CFC-12     102     1  -  2     2            CCl2F2
HCFC-22    112     1  1  2     1            CHClF2   
HCFC-123   213     2  1  3     2            CHCl2-CF3
HFC-134a   224     2  2  4     -            CH2F-CF3

Halons are numbered according to a totally different system developed by
the US Army Corps of Engineers, and the prefix term is always "Halon". 
Hydrogen is not numbered, and terminal zeros are not expressed.

Halon-0123  where 0 = number of carbon atoms
                  1 = number of fluorine atoms
                  2 = number of chlorine atoms
                  3 = number of bromine atoms

Halon-1211 CBrClF2      bromochlorodifluoromethane               [353-59-3]
Halon-1301 CBrF3        bromotrifluoromethane                    [75-63-8]
Halon-2402 CBrF2-CBrF2  1,2-dibromo-1,1,2,2-tetrafluoroethane    [124-73-2]
 
12.4  How can I get the IUPAC chemical name from traditional names?

It depends. Usually the quickest way is to look the name up in a chemical
supplier's catalog, MSDS, or a standard text like Merck or Hawley. You can 
also often find the correct name if you refer to an old chemistry text that 
lists both the traditional and IUPAC naming conventions. Some traditional 
or common names also refer to mixtures of chemicals, eg aqua regia, piranha 
solution.

One reason why traditional names have been replaced is because the same name 
could be used for different compounds. An example is the use of caprylic to 
describe 1-Octanol and 2-Octanol, and attempts to qualify the name with 
"primary" and "secondary" were less than successful. Octyl alcohol has been
used to describe both 1-octanol and 2-ethylhexanol, thus explaining why the
well known dioctyl phthalate (DOP) is actually bis(2-ethylhexyl) phthalate.
The following examples highlight the diversity of names often encountered. 

Carbon   Alkane        Alcohol               Aldehyde         Acid

1        methane       methanol              form-            formic
                       carbinol
2        ethane        ethyl                 acet-            acetic
                       methyl carbinol
3      n-propane       n-propyl              propion-         propionic
                       ethyl carbinol
4      n-butane        n-butyl               n-butyr-         n-butyric
                       propyl carbinol 
5      n-pentane       n-amyl                n-valer-         n-valeric
                       butyl carbinol                  
6      n-hexane        hexyl                 capro-           caproic
                       amyl carbinol         caproic
7      n-heptane       enanthyl              enanth-          enanthic
                       enanthic
                       hexyl carbinol
8a     n-octane        capryl                capryl-          caprylic
                       primary caprylic      caprylic
                       heptyl carbinol
                       1-octanol
8b                     capryl                
                       secondary caprylic
                       methyl hexyl carbinol
                       2-octanol
9      n-nonane        pelargonic            pelargonic       pelargonic
                       octyl carbinol        
10     n-decane        capric                capr-            capric  
                       nonyl carbinol        capric                         
12     n-dodecane      lauryl                laur-            lauric
                       lauric                lauryl        
14     n-tetradecane   myristyl              myrist-          myristic
16     n-hexadecane    cetyl                 palmit-          palmitic
       cetane
18     n-octadecane    stearyl                                stearic 
20     n-eicosane      arachidyl                              arachidic

Primary 
 - alcohol    R1CH2OH
 - amine      R1NH2
 eg normal    straight chain    normal octane     n-octane
                                normal butanol    1-butanol  
    iso       branched chain    iso-butane        2-methylpropane
                                iso-butanol       2-methyl-1-propanol 
                                iso-octane        2,2,4-trimethylpentane

Secondary 
 - alcohol    R1R2CHOH
 - amine      R1R2NH
 eg                             sec-butanol       2-butanol       
                                iso-propanol      2-propanol

Tertiary 
 - alcohol    R1R2R3COH
 - amine      R1R2R3N
 eg                             tert-butanol      2-methyl-2-propanol

- substitution onto the benzene ring
  1,2 = ortho                ortho-xylene
  1,3 = meta                 meta-xylene  
  1,4 = para                 para-xylene

However other names get more tricky, especially historical names, where
several names may be used for the same chemical and, even worse, different 
chemicals can be described by the same name. Examples include:-
- calcium carbonate = limestone, chalk, calcite. 
- calcium hydroxide = slaked lime, hydrated lime, caustic lime.
- calcium oxide = calx, lime, quicklime, unslaked lime, burnt lime.
- hydrochloric acid = muriatic acid, spirits of salts.
- nitric acid = aqua fortis.
- potassium carbonate = potash, artificial alkali, vegetable alkali.
- potassium hydroxide = caustic potash, lye.
- sodium carbonate - any form = soda, natural alkali, mineral alkali.
                   - anhydrous = soda ash.
                   - dodecahydrate = sal soda, washing soda.
                   - monohydrate = soda crystals.
- sodium chloride = rock salt.
- sodium hydroxide = caustic soda, lye, soda lye.
- sulfuric acid = oil of vitriol

Some old chemical terms are seldom encountered these days, but have very 
specific meanings, eg
" flowers " described any product of sublimation, hence "flowers of sulfur".   
" specific " in front of any quantity means " divided by mass ", hence
    "specific gravity".
" ether " described a volatile liquid, not only compounds with the Cx-O--Cy 
    structure, and also often known today as "spirit".
" aromatic " described a liquid that had an aroma, not only those derived
    from benzene, or which benzene ring structure.
" oil " described a liquid that was not miscible with water, thus it 
    described different products in different chemical industries :-
  - Essential oils = volatile and odoriferous liquid plant extracts. 
    Essential oils can be obtained by extraction or distillation ( steam ), 
    often contain terpenes ( based on the isoprene structure ), are usually
    smelly ( aromatic ), and are used for perfumes, flavours and aromas, eg 
    lemon oil and pine oil. 
  - Triglyceride oils = fats and oils based on the glycerol molecule that
    can be obtained from plant and animal material, frequently by melting or
    cold pressing. They are a significant, and important, component in our 
    diet, eg soya oil, lard, fish oils, and anhydrous milk fat. 
  - Petroleum oil = a mixture of a large number of hydrocarbons that are 
    usually derived from 0.1 to 3 billion-year-old organic matter. Crude oil 
    can contain hundreds of hydrocarbons with one to sixty carbon atoms, and
    the hydrocarbons are usually grouped and reported by type, eg alkane 
    ( paraffin ), alkene ( olefin ), or arene ( aromatic ).
   
Almost all old industries had easy-to-remember names for chemicals they
commonly encountered, but today many of those names can cause confusion
if used outside the industry. Some common examples, just from the petroleum 
industry alone are:-
- " ether " is a volatile hydrocarbon fraction that does not contain the 
    Cx-O-Cy structure, eg petroleum ether ( aka petroleum spirit ).
- " naphthene " is a cyclic paraffin, does not contain naphthalene, and is 
    not a major component of naphtha ( refer Section 27.5 ). 
- Benzene, toluene and xylene are often called benzol, toluol, and xylol,
    even though they do not contain an -OH group.
- Benzine ( ligroin ) was a saturated hydrocarbon fraction that boiled 
    between 20C and 135C. Gasoline/petrol fractions are still called benzine 
    by some older people. 
- Diesel fuel is often called "gas oil", which is a historical term for  
    hydrocarbon distillate fractions. Atmospheric gas oil has a boiling 
    range between 220C - 450C, and vacuum gas oil boils from 350C to 550C.  

12.5  What does "omega-3 fatty acids" mean?

Chemists recognise that they should always number carbon chains from the 
end with the functional group, so the location of double bonds in 
unsaturated fatty acids are numbered from the carboxylic acid end, and
are usually designated by "delta" in their abbreviated names.

Biochemists are more interested in the actual role that chemicals play, 
consequently they will consider the position from the end that is important.
In the case of natural fatty acids the double bonds are usually cis
configured, and it is the distance of the first double bond from the
terminal end of the carbon chain that is important. They use "omega" to
signify that the double bond is cis, and they are counting from the other
end. The great advantage is that chain length can be ignored, and compounds
that are subjected to the same biochemical processes are grouped together.

In 1967, the IUPAC/IUB commission responsible for lipid nomenclature 
recommended that for unsaturated fatty acids with cis double bonds, that
the "omega" symbol be replaced with "n-x", where n = the length of the 
carbon chain, and x is the distance from the terminal end.
 
Some examples:-

Common            Chemical                            Chemical    Biochemical
 Name               Name                             d = delta     o = omega

Oleic           cis-9-octadecenoic                    c-C18:1d9     C18:1o9
Elaidic         trans-9-octadecenoic                  t-C18:1d9        -
Ricinoleic      D-(+)-12-hydroxy-octadec-cis-9-enoic  c-C18:1d9-12OH   -
Linoleic        cis-9,12-octadecadienoic              c-C18:2d9     C18:2o6
alpha Linolenic cis-9,12,15-octadecatrienoic          c-C18:3d9     C18:3o3
gamma Linolenic cis-6,9,12-octadecatrienoic           c-C18:3d6     C18:3o6
Arachidonic     cis-5,8,11,14-eicosatetraenoic        c-C20:4d5     C20:4o6
EPA             cis-5,8,11,14,17-eicosapentaenoic     c-C20:5d5     C20:5o3
Erucic          cis-13-docosenoic                     c-C22:1d13    C22:1o9
DHA             cis-4,7,10,13,16,19-docosahexaenoic   c-C22:6d4     C22:6o3

EPA and DHA are widely known as the omega-3 fatty acids present in high
concentrations in marine lipids, and are considered beneficial in diet,
although research is not complete [4,5]. 

12.6  What is Conjugated Linoleic Acid?

Conjugated linoleic acid describes the group of positional and geometric
isomers of linoleic acid ( cis-9,12-octadecadienoic acid ) that have a
conjugated double bond system starting at carbon 9, 10, or 11. They can be
either cis or trans, or various combinations of them. The more abundant
isomers in food are believed to be the cis-9, trans-11, and the trans-10, 
cis-12 isomers. It's very difficult to separate the cis-9, trans-11 and
trans-9, cis-11 isomers, however the cis-9, trans-11 form is usually 
considered the important and usually dominant isomer. 

They are typically produced by bacteria in the rumen of ruminants because
the hydrolysis of fats in the rumen produces more unesterified linoleic
acid than is available to bacteria in other digestive systems. Plants
also contain conjugated linoleic acid, but there is much less of the
cis-9, trans-11 isomer, which is believed to be the biologically active
isomer. Foods that contain CLA are lamb, beef, turkey and dairy fat products,
ranging from 2.5 - 11 mg/g of fat - of which 75% or more is the cis-9, 
trans-11 ( or trans-9, cis-11 ) isomer. CLA is of interest because it has 
displayed antimutagenic activity in animals and human cell tests [6,7].
  
12.7  What are "heavy" metals?

There appears to be no standard definition, however the general consensus
appears to be all metals with a density greater than 4 or 5 [8,9,10]. If 
you also consider the conventional analytical chemistry definition of "heavy 
metals" ( precipitation of sulfides from acidic solutions ), you obtain 
quite a diverse mixture of possible candidates. Moving the density limit 
from 4 to 5 really only just impacts on Ti, Y and Se. Some other texts use 
more complex definitions that may also include accepted "light" metals with 
densities less than 4, eg Hawley uses "A metal of atomic weight greater 
than sodium (22.9) that forms soaps on reaction with fatty acids. e.g., 
aluminum, lead, cobalt". The term " heavy-element " is commonly used to 
describe the transfermium elements, - elements with an atomic number 
greater than 100.
  
12.8  What is the difference between Molarity and Normality?.

A Molar solution contains one gram molecular weight ( aka mole ) of the 
reagent in one litre of solution, and is represented by " M ". In modern 
usage, "molar" is intended to only mean " divided by amount of substance",
and is not supposed to be used to describe 1M solutions. There are already
exceptions to the rule ( molar conductivity, molar extinction coefficient ),
so I would only worry about correct usage in exams, as in the real world
most chemists use Molar to describe 1M solutions.   

A Molal solution is one gram molecular weight of the reagent in 1 kilogram 
of solvent, and is usually represented by "m". This concentration unit is
relatively uncommon in the real world, so it's worth checking that the "m"
is not a "M" typo.    
 
A Normal solution contains one gram equivalent weight ( aka equivalent ) 
of the reagent in one litre of solution, and is represented by " N ". 
The equivalent weight of a reagent may vary according to the reaction, but 
if considering just acid and base moles and equivalents, then:-

1M H2SO4 + 2M NaOH -> 2H2O + Na2SO4    
1N H2SO4 + 1N NaOH -> H20 + 0.5Na2SO4
1N HCl + 1N NaOH -> H2O + NaCl

So you can see that the equivalent weight of an acid is that which contains
1.0078 grams of replaceable hydrogen which, in the case of sulfuric acid, 
would be half the mole weight, but, in the case of hydrochloric acid, would 
be the mole weight.

The equivalent weight of a base is that which contains one replaceable 
hydroxyl group ( ie 17.008g of ionisable hydroxyl ). Thus the equivalent 
weight of sodium hydroxide ( NaOH ) and potassium hydroxide ( KOH ) would 
be the mole weight, but for calcium hydroxide ( Ca(OH)2 ) it would be half 
the mole weight.

The equivalent weight of an oxidising or reducing agent is that weight of 
the reagent that reacts with or contains 1.008 grams of available hydrogen 
or 8.000 grams of available oxygen. "Available" means being able to be 
utilised in oxidation or reduction reactions. The equivalent weight of an 
oxidising agent is determined by the change in oxidation number which the 
reduced element experiences, eg the reduction of potassium permanganate in
dilute H2SO4 gives;-
                              K Mn O4   -->   Mn S  O4  
(Oxidation Number)           +1 +7 -8         +2 +6 -8
This results in a change of the manganese from +7 to +2, so the equivalent 
weight is 1/5 of a mole. However, in neutral solution the change would only 
be 3 because the product is MnO2, giving an equivalent weight of 1/3 of a 
mole. If reacted in strongly alkaline solution the product is MnO4--, giving 
an equivalent weight of one mole. 

The equivalent weight of a reducing agent is determined by the change in 
oxidation number that the oxidised element undergoes. For the conversion of
ferrous sulfate into ferric sulfate;-
                           2 (Fe SO4)  -->    Fe2 (SO4)3
(Oxidation Number)         2x(+2 -2 )       (+3)x2 (-2)x3  
The change in oxidation number per atom of iron is 1, so the equivalent 
weight of ferrous sulfate is 1 mole.

There are wide range of rules about the determination of the oxidation 
number, but if you have been taught to use molarity, I would not bother too 
much about normality, as it is mainly used these days by analytical 
chemists - because it is convenient for many common titrations. Analysts 
assume that 1 ml of 1N reagent will react with 1 ml of 1N reagent. However,
there has been a recent Journal of Chemical Education article that claims
using normality and equivalent weight does help students understand 
chemistry, but those concepts are unlikely to become widespread again [11].

12.9  Where can I find the composition of common named reagents?.

Often the best place to start are MSDS sheets or catalogues from commercial 
suppliers. Some textbooks include a list of named reagents and their 
composition that are mentioned in the text. The very common reagents are 
usually also detailed in Hawley or the Merck Index. One chemistry field that 
has a lot of named reagents is analytical chemistry, especially in Thin Layer
Chromatography, where many of the spray detection reagents have common names.
Merck produces a handy guide describing the composition and production of 
common TLC spray reagents [12].   

Some common reagents include:- 
- aqua regia = 1 part nitric acid and 3 or 4 parts hydrochloric acid.
- piranha solution = highly dangerous ( explodes on contact with traces of 
    organics ), warm (65C), 70:30 mixture of 100% sulfuric acid and 30% 
    hydrogen peroxide. It is used, with comprehensive safety precautions, 
    in the semiconductor industry, and also in some laboratories to clean 
    glassware [13,14,15]. Many chemical laboratories prohibit it, and there
    are much safer, equally effective, alternatives available - refer 
    Section 16.7.   

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