PACIFIC SOUTHWEST ASSOCIATION OF CHEMISTRY TEACHERS SOME DIFFICULTIES AND COMMON ERRORS RELATED TO THE DESIGNATION OF SUGAR CONFIGURATIONS' JOHN LEO ABERNETHY California State Polytechnic College, San Luis Obispo, California
S o m of the confusion in stereoorganic chemistry has arisen owiug to careless~~ess in adhering to certain established rules or conventions concerning configurational representation. Gntil about five years ago, most introductory organic textbooks and certaiu advanced works in organic chemistry were especially in error with regard to the meaniug of the planar configurational formula of the important reference compound Dglycerose (D-glyceraldehyde). The teacher and studeut alike were confront.ed with a uumber of inaccuracies related t o this compound. Other errors of a similar nat,urealsoexist,edinthegeneral field of stereochemistry. Since modern organic chemistry is so vitally concerned mith stereochemistry, it is of value to consider some of these difficulties. The absolute configuration of D-glycerose mas not reported until 1951. However, the planar configurational formula (I) was assigned to this compound loug ago. It was no doubt commonly felt that since the standard for writing this formula was an arbitrary one, you could work backward from it and obt,ain either the three-dimensional model (11) or the model (111). both of which by the arbi'trary starldards &ch happened to be chosen a t the time could he represented by (1). CHO
I
H-C-OH
I
CH,OH
CH,OH
CIH~OH
(1)
(11)
(111)
This, of course, was doue without attention to the real uature of the arbitrary standards set d o r v ~by ~ Emil F i ~ c h e r . ~There are still some reference sources pertaining to organic chemistry that wrongly select model
(111) rather than correctly choosing model (11) to be represented by (I). According to the conventions originating from Fischer, the hydrogen and hydroxyl bouded to the asymmetric carbon of the planar glycerose formula are projected upward from t,he plane, or toward t.he ohserver. Rosanoff3 promoted the r u r r e ~ ~ tused l y convention for the D-series of aldoses. He related these aldoses to n-glycerose. In the D-series the hydroxyl is always to the right on t,he bottom asymmetric carbon when the aldehyde group is a t the top of the vertical chain of carbons. The L-series consists of the antipodes of the D-series. Hence, the hydroxyl is always to the left on the bottom asymmetric carbon in this series when the aldehyde group is a t the top. I
I
(CHOH).
I
01
H-C-OH I
hi^ rule
established because ~ i had ~ previously assiglled the prefix to certain sugars that For could not iustifiahlv be olaced in that cateeorv. " example, Fischer had given the name D-gulose to the gulose antipode that yielded the same saccharic acid as o-glucose. CHO COOH CHO I H-A-OH H-C-OH I HO-OH I 101 [OI I HO-c-H
HO-v-H H-&OH
Presented before the meeting of the Pacific Southwest Association of Chemistry Teachers a t the Univel.sitg of California, Riverside, April 30, 1955. The author is indebted to Professor Norman Kharasch for the use of a reprint of the p.%per"Determination of the absolute configuration of optical antipodes," by BIJVOET, J. M., Endeavour, April, 1955, p. 71. FISCHER, EMIL,Bar., 2 4 , 1836 (1891).
CHO
CHO
-E1O-v-H H-&-OH
I H-C-OH I CH?OH
H-C-OH I COOH
U-GIII(:ORB
Smrharir acid
+ -
H-&-OH
I HO-C-H I CHsOH r.-Gulose (called D-Gulose by Fiseher)
ROSANOW, h1. A,, J . Am. Chem. Soc., 28, 114 (1906). 88
~
h
VOLUME 33, NO. 2. FEBRUARY, 1936
I t was Rosanoff who pointed out that to place two carbohydrates in the same D-series or in the same Lseries merely because they yield the same saccharic acid leads to confusing inconsistencies. The gulose called D by Fischer is obviously L-gulose in Rosanoff's classification because the hydroxyl a t the bottom asymmetric carbon is to the left when the aldehyde group is a t the top of the vertical carbon chain. It was not until recently that J. M. Bijvoet4 suggested that the absolute configurations of the optically active tartaric acids could be determined by means of X-ray analysis of certain of their salts. The possibility that such an analysis might work had long been overlooked but mas imbedded in a statement of von Laues in 1916. Prior to that time it had been assumed by W. L. Brag@ that the phase difference between the waves of two atoms depended only on the path difference between those atoms, and that the nature of the at,oms had no influence on the phase. von Laue wrote that it would be iuteresting to see whether an exception could be established in cases where the frequency of the incident X-ray radiation lies near a naturalfrequency of the atoms. The idea proposed by von Laue was tested in 1930 by Coster, Knol, and P r i m 7 They used a zinc sulfide (zinc hlende) crystal for analysis, and the X-rays produced in an X-ray tube having a gold target for the cathode rays. The Lal radiation of gold just excited the K electrons of zinc. The resultant anomalous scattering permitted the determination of whether the crystal was being viewed in the ZnS-ZnS direction or in the SZn-SZn direction; in other words, the polarity of atomic succession was found through the aid of anomalousdiffraction. Xormal diffraction cannot be used to distinguish between mirror-image crystals, or antipode molecules. During the years from 1930 to 1950 it was even generally felt that it was essentially impossible to assign absolute configurations t o antipode molecules by means of X-ray analysis. I n 1949 J. M. Bijvoet4 made public the statement that by means of anomalous diffraction even absolute configurat,ions could be established. This statement was followed up in 1951 with experimental work establishing the absolute configurations of the dextro and leuo tartaric acids. BijvoetSemployed the sodium rubidium tartrate dihydrate (NaRbC4HaOs. 2H20) prepared from dextrorotatory tartaric acid. Excitation of the rubidium atom was accomplished by X-rays from a zirconium target. In other words, the Ka X-rays from the zirconium had frequencies in the absorption edge of the K elect,rons of the rubidium atoms. The difference in patterns that would be caused by the salts of dextrorotatory and levorotatory tartaric acids, as a consequence of anomalous diffrac-
09
tion, was predicted with t,he aid of quantum mechanics. The particular pattern obtained by Bijvoet for the salt he used corresponded to that predicted for the salt of the ~(dextro)-tartaricacid of Emil Fischer's conventions. Hence, Emil Fischer's arbitrary conventions turned out to be the absolute ones; or stated differently, by accident they corresponded to reality. There is still a tendency for a novice in the field of stereochemistry to use the terms dextro and D interchangeably, as well as the terms leuo and L. It is particularly evident, now that some absolute configurations have been found, that the D and L terms have reference to configurations whereas dextro and levo, respectively, indicate dextrorotatory and levorotatory substances. One of the examples most often used in clarification of this point is the oxidation of D-glycerose to D-glyceric acid. Whereas the configuration obviously does not change through oxidation, because the hydrogen and hydroxyl joined to the asymmetric carbon atom are not altered in configurational bonding, the sign of rotation does change.
~
0
C-H
C-OH
II
II
+
Dextro and are interchangeable and so are leva and -. Dexcro and leu0 mean rotation of the plane of polarized light t o the right and to the left, respectively, as the observer looks toward the plane of polarized light through the substance analyzed; and - designate the signs of the degrees of rotation given a t the eye piece of the polarimeter. The plus and minus signs avoid the flaws inherent in t,he theoretical conception of a "plane of wave motion of light" and its being turned by passing through an optically active material. Instead, signs can be given to the degrees of rotation of the eye piece necessary to restore matching fields of light a t the eye piece of the instrument, after the electromagnetic energy called plane polarized light has entered a substance and the electromagnetic energy that exits gives matched fields once more. This distinction be-
+
CHO I HO-C-H
CHOH
I
HCN L
HO-C-H
1
CH~OH 7.-Glyrerose
' BIJVOET,J. M., Proe. Aead. Sci. Amsterdam, 52, 313 (1940). V O K LAUE,M., Ann. Physik., 50, 433 (1916). ' BRAGG,W. L., Physik. Z., 15, 7 i (1914). 7
0
COSTER, D., K. S. KNOL,AND J. PRINS,Z . Physik, 63, 345
1930).
PEEEDEMAN, A. F.,A. J. VAN BOMMEL, AND J. M. B~JVDET, Proe. A d . Sn'. Amsterdam, B 54, 16 (1951).
COOH
I
CHOH HO-C-H I
CH?OH
I
CHlOH
COOH
I
HOH ----t
YOOH
HO-A-H
H-C-OH
I01 A
I
HO-q-H
+
I
RO-7-H
I
COOH deztroTartaric acid (absolute)
I
COOH msD-
Tartaric acid
JOURNAL OF CHEMICAL EDUCATION
90
tween deztro and D, as well as leva and L, is needed in relating the glyceroses to the tartaric acids. The arbitrary configurations given to D-glyceroseand D-glyceric acid are now absolute ones because deztrotartaric acid can be related, in theory, to L-glycerose through the above chemical reactions. D-Glycerose is, therefore, of the same absolute configuration as lewotartaric acid. Also, it is evident, because of wellestablished reactions and Rosanoff's conventions, that D-glucose has the absolute configuration represented as follows:
have difficulty in arriving at three-dimensional models from the planar configurational formulas labeled as ambiguous. At carbon No. 5 it is evident that the hydrogen and ring oxygen are projected toward the observer. At carbon one, or the hemiacetal carbon, both a ring oxygen and a hydroxyl are present. It would be a question as to whether the hydrogen and ring oxygen or the hydrogen and hydroxyl are to be projected toward the observer, while maintaining their right and left relationships shown by their written planar configurations. Actually, the hydrogen and hydroxyl are projected toward the observer. By bondCHO CHO ing the ring oxygen from above the top carbon, thereby I making it essentially a part of the apparent carbon H-C-OH I chain, the projection of hydrogen and hydroxyl at HO-C-H carbon No. 1 of the formulas labeled unambiguous can I be tackled in the same way as at the other carbons. H-C-OH I Diastereoisomers are optical isomers whose conH-C-OH figurational formulas can be divided into two opt,ical I CH.OH portions, one portion of which has the same configuration in each molecule, but the other portion involves Acyclic o-glucose Acyclic glucose (three-dimensional) (planar) mirrored configurations. Alpha and beta modifications of a particular sugar, of specified ring size, are Once the meanings of D, L, dextro, and leva are underordinary diastereoisomers. They differ in configurastood, the problem of ring configurations of sugars tion only at the hemiacetal positions. It is customary can be considered. When the carbonyl group enters to refer to such an alpha and heta pair as anomers. into ring formation, a new asymmetric carbon is proI n the D-series, the anomer with the more positive speduced with a hydroxyl radical joined to it. I n the cific rotation is the alpha isomer, while the beta isomer case of D-glucose, two compounds result with sixhas the less positive rotation. The L-series is commembered or pyranose rings, namely a-D-glucopyranose prised of the mirror forms of the D-series. Since each and 8-D-glucopyranose. This results when the acyclic single antipode has a specific rotation equal but opmolecule undergoes intramolecular hemiacetal formation. In writing planar formulas, ambiguous and posite in sign to its mirror form, it follows that in the unambiguous methods can be, and often are, employed. meries the alpha isomer of an anomeric pair has the more neeative rotation and the beta isomer has the less negative rotation. Usually the alpha anomer will be H OH the one with the hemiacetal hydroxyl on the same side \ / rc--l H-C-OH as the oxygen of the bottom asymmetric carbon when the hemiacetal is toward the top of the chain; the heta H-A-OH H-c--oN anomer usually has the hydroxyl of the hemiacetal on I I I 0 HO-C-H 0 HO-C-H the opposite side from the oxygen of the bottom asymmetric carbon. That oxygen of the bottom asymmetric H-A-OH H-C-OH carbon may be involved in the ring, as in the auomeric pyranose forms of D-glucose, or that oxygen may be a I I CH4)H CH20H part of a hydroxyl group, as occurs in the anomeric Ambiguous Unamhiguaus furanoseforms of D-glucose.
-
~~
~~~
~~~
~~~
~
~
~~~
I
I
a-D-G!ucop\.r;mosc
HO
H \ /
c-
1
H-&OH I
Ho-c-H
I
H-C-OH
11
HO-CT I
o
H(j-dlS--A
H-C-OH
I
H-&OH
H-C
I
HO-C-H
()
I
H-C-OH
I
I H - C L
0
I
I
I
CHIOH CWH?OII Amhignous Unamhiguous 8-D-Gluoopyrano~e Planar configurxtional formulas
I n the case of the alpha and bet.a situations, one might
I n the case of the glycosides, the same rules of rotational values and configurational assignment hold as do with the hemiacetal sugars themselves. The only structural difference between glycosides and these
VOLUME 33, NO. 2, FEBRUARY, 1956
91
hemiacetals is that -OR replaces hemiacetal -OH. I t should be emphasized that it does not necessarily follow that, if the specific rotation is more positive in the n-series for a given glycoside or a given cyclic form of a sugar, the alkoxy group or hydroxyl will be on the same side as the oxygen of the bottom asymmetric carbon; it only means that the particular isomer in the wseries must be called alpha because it has a higher G,OH specificrotation than its anomer. Correct (A) Correct ( B ) Incorrect (C) For many purposes, three-dimensional models are valuable in formulating chemical reactions. Haworths Correct Heworth models used the system of expressing the furanose or pyranose planar ring in a horizontal, coplanar manner, with hydrogens, 8-D-Idofuranoserepresentations hydroxyls, and carbon-chain residues projected vertically above or below the plane of the ring. He formu- the configuration must he represented in a planar manner at that position. Therefore, when carbon No. 5 is lated &~(deztro)-glucopyranose in this way: downward from the ring, its configuration is represented exactly as carbon No. 5 is shown in the planar formula. On the other hand, Haworth model ( B ) is also correct because carbon No. 5 is projected upward from the ring; the same thing would result if carbon No. 5 of the planar formula had the primary alcohol group placed a t the top of the vertical chain and the aldehyde at the bottom, with a correct retention of configuration for the Carbon Nos. 2 and 3, in this particular model, are pro- entire molecule. I t in evident, therefore, that the jected outward from the plane, while carbon No. 5 is Haworth model (C) is wrong because the hydroxyl at projected into the plane. The atoms or groups joined carhon No. 5 must be to the left when carhon No. 5 is vertically to the ring carbons were understood to projected upward from the ring. I n passing, it should project slightly outward from the ring, in order to place be noticed that, the hydrogens bonded at carbon Nos. 3 each ring carbon as nearly in the center of a tetrahedron and 4 of the Haworth models are correct in their cis rclationship, whereas they appear to be trans in the as permissible. Comparison of the unambiguous planar configura- planar formula. The alpha and beta anomers of D-fructofuranose tional formula of 8-D-glucopyranosewith the Haworth three-dimensional model reveals another peculiarity display another difficulty in planar representation. often overlooked. The hydrogens a t carbon Nos. 4 and Customarily, these molecules are represented in this 5 of the planar formula are written on the same side, way: thus giving conformity to Fischer's rules of projection. HOCHXOH HO CHrOH I/ The Haworth model shows those two hydrogens artu\I C--, -C ally to be on opposite sides of the ring. This is due to the fact that in forming a ring from an acyclic D-glucose HO-A-H HO-C-H model, a twist about carbon No. 5 is necessary, thereby causing this apparent discrepancy. This is always true H-C H-C of acyclic models. When the nth carbon down the I I chain is asymmetric and is joined to the ring oxygen, CHrOH CHlOH the apparent cis or trans relationships of the hydroa-o-Glueofuranose 8-D-Glucofuranose gens a t the nth and (n - 11th carhons of the planar Ordinary representation formulas are opposite from the actual trans or cis relaAgain, it might be a question as to whether the ring tionships in the Haworth models. oxygen or the hydroxyl at carbon two should be proAnother error that shows up concerns those iustances in which a Haworth type of formula has a residual chain jected toward the observer. The ring oxygen could be of carbons joined to the ring, with an asymmetric car- honded from above, while the hydroxymethyl radical bon in the residue. Since the configuration of this might he bonded to the side. residue must be represented in a two-dimensional way, the hydroxyls of the residue must be represented in I accord with Fischer's conventions. For example, corHO-C-H HO-C-H rect and incorrect models of 8-D-idofuranose are com41 0 H-c-OH 1 d - o pared with the planar configuration. The focal point is carhon No. 5. In the correct Haworth model ( A ) , rarFI-C H L ei bon No. 5 has the bonded hydroxyl to the right because I
1
j
CHaOH a-o-Frnrtofuranose
CH20H 8-D-Fructofuranose
JOURNAL OF CHEMICAL EDUCATION
92
By writing the hydroxymethyl group to the right or to t,he left a t carbon No. 2, it is theu clear that these twodimensional formulas would be transferred into the following three-dimensional models:
placed at the top of the vertical chain of carbons, since the hydroxyl is still on the right at the bottom asymmetric carbon. There are numerous instances in which the absolute configuration of a molecule is known hut a D or L assignment to the configuration is arbitrary. An example in point is leuo-sec-butyl alcohol, whose ahsolute configuration is known through this reaction sequence:
-
CHO
1
[O]
H-C-OH
COOH
I 1
PBlz -L then HOH
H-C-OH CHaOH
I n transferring the planar models to the threedimensional ones, of course, a trans relationship of hydrogens a t carbon Nos. 4 and 5 is produced. The alpha and beta terms have reference, respectively, to higher and lower specific rotations in the D-series. Still unsettled for certain chemists is the matter of assignment of the D and L prefixes to the tartaric acids. Whereas Wohl assigns a D prefix to the levorotatory form, Freudenberg- gives t,his same form an L prefix. HO-C-H 1
H-C-OH
I
H-C-OH I
HO-b-~
Hn I + H-C-OH Pt
CH&
IriAIH4
CH?OH
I
H-c-OH I
PBrs
COOH
COOH
I
1 1
H-C-OH
hydrol. L
CHGOOH
I
H-C-OH
CHnBr
H-A-OH
I
CHa D(-)Lactic Acid
-
I
A
I
LiAlH,
CHSCN
KCN
H-c-OH I
CH1CH90H
1
H-?-OH
PI3 ----t
I
COOH Dextrorotary ~(dezt~o)-Tartaric acid (Wohl) acid ~(1ew)-Tartaricacid (Freudenherg) ~(de3-lro)-Tartarir (Freudenbere)
AOOH Levorotrttory o(leoo)-Tartaricacid (Wohl)
The Wohl designation is the one ordinarily employed a t the present time. For a long time, dextrorotatory tartaric acid was assigned the D prefix because it could be obtained by a direct oxidation of D-glucose. (
CHO
I
H-C-OH I
H-c-OH
COOH I
COOA
I CHzOH
Dextrorotatory tartartie acid
Rosanoff, in 1906, insisted: "The direct oxidation which produces ordinaryIO tartaric acid from D-glucose is scarcely a more reliable criterion than would be a process of d e s t n d v e distillation." The Wohl system ought to win out because in his procedure the hydroxyl on the bottom asymmetric carbon is to the right for the D antipode, just as in the case of the Dsugars. I t makes no difference, in the case of the levorotatory tartaric acid, which of the carboxyls is Author's correction added in proof: the positions of the OH and H on the Nos. 3 and 4 carbon atoms should be reversed. ' 0 By "ordinary" ia meant the readily available devtrarotrttory farm.
- )-sec-Butyl alcohol
The hydroxyl can he written to the right or to the left. If one were to follow the rule that the asymmetric carbon should be placed as near to the bottom of the chain as possible, then this would be D(-)-see-butyl alcohol because the hydroxyl is t o the right under such conditions. No such rule has been established. Still, most people assign the D prefix to this particular antipode. An intimate knowledge of organic chemistry and substitution reactions is needed to be able to assign a D or L prefix t o substances like the alanines and a-chloropropionic acids. The L-series with relation to the known L-lactic acid is this: COOH I
NH*-C-H I CH~ L-Alrtnine
COOH
CI-A-H
I
CHs >a-Chloropropionie acid
COOH
HO-A-H
I
CHa >Lactic acid
Absolute configurations of the optically active hiphenyls like 6,6'dinitro-2,2'-diphenic acid are as yet unknown.
VOLUME 33, NO. 2, FEBRUARY, 1956
A NO,
N &
COOH
93
w
acids. Any carbon chosen* could have its hydroxyl to the right orto the left.
COOH
Even if they were known, there would be no way t o classify the antipode acids as D or L. The same thing is true of substances such as the camphor antipodes. It would be very difficult to establish a rule for giving a D or L prefix t o levo-inositol. Its absolute configurat,ion is kuown through oxidation to certain saccharic
H
H "
OH
lmo-Inositol
Any carbon could be placed a t the bottom by rotating the ring about its center like a wheel.
BY ANALOGY ANALOG computers are being
u ~ e dincreasingly as "simulators" for system design problems and industrial process control. I n contraat to digital computing machines, which work with actual numbers (digits) and achieve their results by making a. great number of "yes" or "no" choices, the analog instruments operate on electrical or meohanicnl analogs of the quantities aetusll.v measured. Thus a slide rule, which multiplies by adding logarithms, is an analog computer. (The words analog and loyarilhm both derive from a root that implies proportion or similarity.) The distance along the scale of a slide rule from 1 to 2 represents, or is an analog of, the logarithm of the number 2. If there is added to this a distance corresponding t o the logarithm of the number 3, the over-all distance measured out corresponds to the number 6 ; multiplication has been achieved by a meohtlnical annlogy to s msthematicsl process. Similarly, nomhern may he represented by such directly measurable quantities as voltages, resistances, shaft rotations, etc.; M. I. T.'s first "differential analyzer," built in 1031, operated on mechanical principles. Many problems in both research and industry can be handled on either andog or digital computers. For olericsl systems, however, or any problem where results moat be expressed in many figures, with grcat accuracy, x digit,al machine ia generally used, either throughout thc problcm 01. sftev :In approximate solution has been determined hy the analog eamput,er. Thus it, would be possible, for example, to cslculato stresses a t various points of an airplane model, under many different wind conditions, by either analog or digital techniques. Rut if the initial data are limited as to accuracy, a suitable range of sizes for st,nlaturd members oan first he found rapidly by analog techniques, and then s. final solution can be obtained, t o much greater aceuracv, by using more refined data, fed int,o x digital computer. Analog computers have found their greatest application to dat,c in haadling engineering design problems. Analog development started around 1938, to simulate presmrr, flow, and temperature measmements in process control syst,ems. Later, analog computers wero used far machine and aerodymmir design, for studying aircraft eont,rol and missile systemrr, and for training pilots, radar operators, and weapon crews. Accuracy of these e d y ~imulatorswas ~&t,isfaetolv for the purpo~e,and well within the limits of precision of the data employed. As the devices were refined for anti-airoraft fire aontrol, socursey and speed became more important, since oomputation had to be made while the radar information from the target was coming in and the guns were being trained. Components for such eqnipmcnt now have sn xrmn.ltry of 0.2 per cent or hetkr. TESTING VARIABLES
Analog computers ma.v he errangod to simuletu or parallel n continuous process and to give continuous qualitative resultsfor example, in terms of pressure, voltage, or speed. Each of
the variable factors in a. process-temperature, pressure, color, acidity, etc.-may be represented by a. voltage fed into the oomputer; reaction with other input voltages simulates the actual conditions of the process. By varying the input,s s t will, the opemtor of the snalog computer csn predict the outcome of any combination of variables with useful accuracy-usually to the fourth decimal place. As one example, itnalysis by analog cornputstion was recently applied to a new generator for a n escort carrier, which was satisfactory in initial tests, hut developed excessive vibration when operating under full power a t sea. Under ordinary circumstances, correction wouldnecessitate making several changesin the size and rigidity of the supporting struoture and observing the effect; such a program would obviously be costly and would take time. With an analog simulator, 16 different modifications were t,ried out within five hours, and the solution offered by the simulator corrected the difficulty.
PILOT STUDIES
I n the chemical industry, the low-cost analog computer can supplement or substitute for the pilot plant, permitting the simultaneous trntine of a. numher of variables without iuterru~tinnthe 11i-mess. In one test. simulated runs of a nrocessine mlant in-
.
savings were realized in terms of raw materials and avoidance of down time; in other oases, analog studies permit experimentation under otherwise difficult conditions. For studies of nuclear reector control, abnormal operations or failures may be simulated safely with analog equipment, where reproducing the actual aonditions of failure could he impassibly dangerous. In general, digital computers m e expensive, justifiable only wherc handling large numbers of digits is necessary. A mediumsised one may coat from $fiO,OOO to $300,000; the "giant brains" cost more t.han $I million and arc capable of eight-figure securaay. Analog computers, while less accurate, are usually much cheaper ($5000 to $200,000). There hits been consklerahle speculation shout the possibility of aonlvine cornouter comoanents to actual mrocess and machine . control and t o materials handling-the "automstie factory." Existing process controls involve many specialized analog devices-meahanical linkages, dials, etc.-that are accurate enough to he used with human nupervision. It is conceivable that digital machines may he combined with analog instruments to obtain en over-all control synt,em. Settings on individual snalog control cin:uits could he supervised and adjusted by the digital eomputer, in order to optimize the over-all working of the plant.Reprinted from the Industlid Bulletin of Arthw D. Little, Znc.
..
.
