THE FACTS ON FILE DICTIONARY OF ORGANIC CHEMISTRY
CONTENTS ENTRIES A TO Z THE VOLUME OF THE GAS THEORETICALLY BE- COMES ZERO IN PRACTICE SUBSTANCES BECOME SOLIDS AT THESE TEMPERATURES; HOWEVER, THE EXTRAPOLATION CAN BE USED FOR A SCALE OF TEMPERATURE ON WHICH –273 15°C COR- RESPONDS TO 0° (ABSOLUTE ZERO) THE SCALE IS ALSO KNOWN AS THE IDEAL-GAS SCALE; ON IT TEMPERATURE INTERVALS WERE CALLED DEGREES ABSOLUTE (°A) OR DEGREES KELVIN (°K), AND WERE EQUAL TO THE CELSIUS DEGREE IT CAN BE SHOWN THAT THE ABSOLUTE TEMPERATURE SCALE IS IDENTICAL TO THE CURRENTLY USED THERMODY- NAMIC TEMPERATURE SCALE (ON WHICH THE UNIT IS THE KELVIN) ABSOLUTE ZERO THE ZERO VALUE OF THER- MODYNAMIC TEMPERATURE; 0 KELVIN OR –273 15°C SEE ABSOLUTE TEMPERATURE ABSORPTION 1 A PROCESS IN WHICH A GAS IS TAKEN UP BY A LIQUID OR SOLID, OR IN WHICH A LIQUID IS TAKEN UP BY A SOLID IN ABSORP- TION, THE SUBSTANCE ABSORBED GOES INTO THE BULK OF THE MATERIAL SOLIDS THAT ABSORB GASES OR LIQUIDS OFTEN HAVE A POROUS STRUC- TURE THE ABSORPTION OF GASES IN SOLIDS IS SOMETIMES CALLED SORPTION THERE IS A DIS- TINCTION BETWEEN ABSORPTION (IN WHICH ONE SUBSTANCE IS ASSIMILATED INTO THE BULK OF AN- OTHER) AND ADSORPTION (WHICH INVOLVES AT- TACHMENT TO THE SURFACE) SOMETIMES IT IS NOT OBVIOUS WHICH PROCESS IS OCCURRING FOR EXAMPLE, A POROUS SOLID, SUCH AS ACTI- VATED CHARCOAL MAY BE SAID TO ABSORB A LARGE VOLUME OF GAS, BUT THE PROCESS MAY ACTUALLY BE ADSORPTION ON THE HIGH SURFACE AREA OF INTERNAL PORES IN THE MATERIAL 2 THE PROCESS IN WHICH ELECTROMAGNETIC RADIATION, PARTICLES, OR SOUND WAVES LOSE ENERGY IN PASSING THROUGH A MEDIUM AB- SORPTION INVOLVES CONVERSION OF ONE FORM OF ENERGY INTO ANOTHER ABSORPTION SPECTRUM SEE SPECTRUM ACCELERATOR A SUBSTANCE THAT INCREASES THE RATE OF A CHEMICAL REACTION IN THIS SENSE THE TERM IS SYNONYMOUS WITH CATALYST IT IS COMMON TO REFER TO CATALYSTS AS ‘ACCELER A ACCEPTOR IT IS ALSO POSSIBLE TO HAVE ‘MIXED’ ACETALS WITH THE GENERAL FORMULA CR1R2(OR3)- (OR4) NOTE THAT IF THE ACETAL IS DERIVED FROM AN ALDEHYDE, THEN R1 AND/OR R2 MAY BE A HYDROGEN ATOM THE MECHANISM OF FORMATION OF AN ACETAL FROM A HEMIACETAL IS ACID CATALYZED IT INVOLVES PROTONATION OF THE –OH GROUP OF THE HEMIACETAL FOLLOWED BY LOSS OF WATER TO FORM AN OXONIUM ION, WHICH IS ATTACKED BY THE ALCOHOL MOLECULE FORMERLY IT WAS CONVENTIONAL TO USE THE TERMS ‘HEMIACETAL’ AND ‘ACETAL’ FOR COM- POUNDS FORMED BY REACTION BETWEEN ALDE- HYDES AND ALCOHOLS SIMILAR REACTIONS BETWEEN KETONES AND ALCOHOLS GAVE RISE TO COMPOUNDS CALLED HEMIKETALS AND KETALS CURRENT NOMENCLATURE USES ‘HEMIACETAL’ AND ‘ACETAL’ FOR COMPOUNDS DERIVED FROM EITHER AN ALDEHYDE OR A KETONE, BUT RESERVES ‘HEMIKETAL’ AND ‘KETAL’ FOR THOSE DERIVED FROM KETONES IN OTHER WORDS, THE KETALS ARE A SUBCLASS OF THE ACETALS AND THE ACENAPHTHENE HEMIKETALS ARE A SUBCLASS OF THE HEMIAC- ETALS ACETALDEHYDE SEE ETHANAL ACETAMIDE SEE ETHANAMIDE ACETATE SEE ETHANOATE ACETIC ACID SEE ETHANOIC ACID ACETONE SEE PROPANONE ACETONITRILE SEE METHYL CYANIDE ACETOPHENONE SEE PHENYL METHYL KE- TONE ACETYLATION SEE ACYLATION ACETYL CHLORIDE SEE ETHANOYL CHLORIDE ACETYLCHOLINE (ACH) A NEUROTRANSMIT- TER FOUND AT THE MAJORITY OF SYNAPSES, WHICH OCCUR WHERE ONE NERVE CELL MEETS AN- OTHER ACETYLENE SEE ETHYNE ACETYL GROUP SEE ETHANOYL GROUP ACETYLIDE SEE CARBIDE ACETYL COA (ACETYL COENZYME A) AN IM- PORTANT INTERMEDIATE IN CELL METABOLISM, PARTICULARLY IN THE OXIDATION OF SUGARS, FATTY ACIDS, AND AMINO ACIDS, AND IN CERTAIN BIOSYNTHETIC PATHWAYS IT IS FORMED BY THE REACTION BETWEEN PYRUVATE (FROM GLYCOLY- SIS) AND COENZYME A, CATALYZED BY THE EN- ZYME PYRUVATE DEHYDROGENASE THE ACETYL GROUP OF ACETYL COA IS SUBSEQUENTLY OXI- DIZED IN THE KREBS CYCLE, TO YIELD REDUCED COENZYMES AND CARBON DIOXIDE ACETYL COA IS ALSO PRODUCED IN THE INITIAL OXIDA- TION OF FATTY ACIDS AND SOME AMINO ACIDS OTHER KEY ROLES FOR ACETYL COA INCLUDE THE PROVISION OF ACETYL GROUPS IN BIOSYNTHESIS OF FATTY ACIDS, TERPENOIDS, AND OTHER SUB- STANCES ACETYL COENZYME A SEE ACETYL COA ACETYLSALICYLIC ACID SEE ASPIRIN ACH SEE ACETYLCHOLINE ACHIRAL DESCRIBING A MOLECULE THAT DOES NOT HAVE CHIRAL PROPERTIES; I E ONE THAT DOES NOT EXHIBIT OPTICAL ACTIVITY ACID A SUBSTANCE THAN CONTAINS HYDRO- GEN AND DISSOCIATES IN SOLUTION TO GIVE HY- DROGEN IONS: HA ˆ H+ + A– MORE ACCURATELY, THE HYDROGEN ION IS SOL- VATED (A HYDROXONIUM ION): HA + H2O ˆ H3O+ + A– STRONG ACIDS ARE COMPLETELY DISSOCIATED IN WATER EXAMPLES ARE SULFURIC ACID AND TRI