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Siibmiinng a sinicture to a calculation can be expensive in terms ol hnmati time and elTort. HyperChem lets you build and display inolecn les easily. Since IlyperCh em con tains a graph ical in lerface. you can monitor the con sirnction ofmoleciiles. 

United Atom force fieldsare used often for biological polymers. In th esc m oleciiles, a reduced ii nm ber of explicit h ydrogen s can have a notable effect on the speed of the calculation. Both the BlOn and OPLS force fields are United Atom force fields. AMBER con tain s both aU nited and an All Atom force field. 

MIXDO/3 is the earliest of the Dewar methods. It provides more accurate geometries and heats of formation than CNDO or INDO. and has been used widely. The limitations of the INDO approximation, on which MI lhO/3 is based, frequently lead to problems of accuracy wdi cri dealing w i th m olecules con tain ing h eteroatorn s. 

Th e force field section (for example am her ) con tain s four en tries ... 

Example. Dissolve 0 3 g. of benzoic acid in a minimum of hot water (about 70 ml.) and add 5% aqueous sodium hydro.xide until the solution is just alkaline to methyl-orange, then add i drop of dilute hydrochloric acid. Pour this solution of the sodium salt into a solution of 0 5 g, of benzylthiouronium chloride in 5 ml. of water, and cool the stirred mixture in ice-water. Filter off the benzylthiouronium salt which has separated, and recrystallise from ethanol con taining 10% of water cream-coloured cr> stals, m.p. i66 . (M.ps., pp. 543 545.)... 

The tap T2 is now closed. The furnace is switched off and the carbon dioxide generator left on until the combustion tube is cold this ensures that the reduced copper spiral, by cooling in carbon dioxide, is main tained in the reduced state. (Despite this precaution it does become spent and should be replaced from time to time. A spent copper spiral leads to high results, but before this takes place there is usually suffici-... 

As just noted (Section 2 7) CH3 is called a methyl group In addition to having methyl groups at both ends n butane contains two CH2 or methylene groups Isobutane con tains three methyl groups bonded to a CH unit The CH unit is called a methme group... 

Many compounds contain more than one functional group Prostaglandin Ei a hormone that regulates the relaxation of smooth muscles con tains two different kinds of carbonyl groups Classify each one (aldehyde ketone carboxylic acid ester amide acyl chloride or acid anhydride) Identify the most acidic proton in prostaglandin Ei and use Table 1 7 to estimate its pK ... 

The lUPAC rules permit cer tain common alkyl group names to be used These include n propyl isopropyl n butyl sec butyl isobutyl tert butyl and neopentyl (Section 2 13)... 

The uncatalyzed addition of hydrogen to an alkene although exothermic is very slow The rate of hydrogenation increases dramatically however m the presence of cer tain finely divided metal catalysts Platinum is the hydrogenation catalyst most often used although palladium nickel and rhodium are also effective Metal catalyzed addi tion of hydrogen is normally rapid at room temperature and the alkane is produced m high yield usually as the only product... 

When bromine adds to (Z) or (E) 2 butene the product 2 3 dibromobutane con tains two equivalently substituted chirality centers... 

Section 11 21 Species with six tt electrons that possess special stability include cer tain ions such as cyclopentadiemde anion and cycloheptatnenyl cation... 

Much of the chemistry of diols—compounds that bear two hydroxyl groups—is analo gous to that of alcohols Diols may be prepared for example from compounds that con tain two carbonyl groups using the same reducing agents employed m the preparation of alcohols The following example shows the conversion of a dialdehyde to a diol by... 

An azeotropic mixture con tains two or more substances that distill together at a con stant boiling point The benzene-water azeotrope contains 9% water and boils at 69 C... 

The strength of this bonding depends on the kind of ether Simple ethers form relatively weak complexes with metal ions but Charles J Pedersen of Du Pont discovered that cer tain polyethers form much more stable complexes with metal ions than do simple ethers Pedersen prepared a series of macrocyclic polyethers cyclic compounds contain mg four or more oxygens m a ring of 12 or more atoms He called these compounds crown ethers, because their molecular models resemble crowns Systematic nomencla ture of crown ethers is somewhat cumbersome and so Pedersen devised a shorthand description whereby the word crown is preceded by the total number of atoms m the ring and is followed by the number of oxygen atoms... 

Enamines are used as reagents in synthetic organic chemistry and are involved in cer tain biochemical transformations... 

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