JPS6237738A - Recording and preserving method for information on chemical reaction - Google Patents

Abstract

PURPOSE:To record and preserve the information on the structural change of chemical substance so that they can be processed by a computer, by discriminating the connections between nodes existing in common and peculiar to the structures of the starting substance and the produced substance. CONSTITUTION:When the hydrolysis, etc. is applied to ethyl acetate, for example, according to the reaction formula I, the numbers 1-11 are added to the nodes of atoms and the atomic groups of the structure of the starting substance based on the formula II. For the structure of the starting substance end the produced substance which are topologically put on each other, the common node connections are shown by the solid lines together with the node connection proper to the produced substance only shown by the dotted lines and the node connections proper to the starting substance only shown by another type of lines respectively. Thus a false transition structure shown in the formula III is obtained with connections shown with discrimination. In such a simple constitution or based on a list of these structures, the information on the structural change of the chemical substance can be recorded including the starting substance and the produced substance so that they can be processed by a computer without increasing the recording capacity.

Description

[Detailed Description of the Invention] [Field of the Invention] The present invention relates to a method for recording and storing information on chemical reactions, and more particularly, to a method for recording and storing information on structural changes in substances related to chemical reactions. It is something.

[Technical background of the invention] In recent years, with the development of computers.

Various methods have been proposed and are being used to record structural information on chemical substances, especially organic compounds. A huge amount of organic compounds and organic chemical reactions have been studied and elucidated to date, but it is possible to effectively use this known information to quickly search for known chemical substances or chemical reactions. Furthermore, it is desired to find a method for synthesizing new substances having desired properties. for that purpose,
Instead of conventional chemical structural formulas, which allow engineers to easily understand the structural characteristics of chemical substances and chemical reactions, we now use expressions that can be processed by computers (that is, computers can make logical decisions). developed,
is required to be used.

The method for recording chemical substances is W L N (Wisw
Typical methods include linear notations such as esser Linear Notation (Esser Linear Notation) and methods using join tables.
S, R, Heller, R, J, Feldmann,
E. Hyde (Eds): “Computer
Representati.

n and Manipulation of Che
"Mical Information" (Jobr+
Wiley and 5ons, New York,
1974). concatenation table
For example, an action table is a list of the types of atoms in the structural formula of a chemical substance, the atoms to which they bond, and the types of bonds.
:It has the advantage of being able to search for chemical substances in units of atoms compared to the linear notation method shown below.

In addition, methods for recording information regarding structural changes (chemical reactions) of chemical substances have also been proposed, but so far no satisfactory expression method is known.
One way to record information about chemical reactions is to use reaction codes.

Specifically, J. Valls, O.5cheiner:
'C: Chemical Information S
systems″, E, Ash, E, )Iyde(
Eds), (Ells Horwood Lim1
ted, 1975) p. 241-258, MJ, L., Obeck, Angew, C.
herB, Intern.

The method described in Ed, Engl., 9.578 (1970), and H.J., Ziegler, J.C.
hem, Inf, Compute.

There is a method described in Sci., 19.141 (+979). This method has a drawback in that it cannot record new chemical reactions when they are discovered, since the viewpoint of chemical reaction expression is fixed. Another drawback is that structural information on chemical substances and information on changes thereof are recorded in separate formats, making it impossible to perform an effective information search.

Another known method is a recording method devised by researchers who design synthetic routes for chemical substances. For example, El, Core
y, R.D., Cramer, W.J., Howe;
J, Am, Chem, Sac,, 94.440
(1972), 1. l1g1. Bauer, J.
J., Braodt, J., Fr1edrich, J.
, Gasteiger, Llochum.

W, 5chubert, Angew, Cheva,
Intern, Ed, Engl.

18, l1l (1979).

However, this method is not suitable for recording individual chemical reactions.

[Summary of the Invention] An object of the present invention is to provide a novel method for recording and storing information regarding structural changes of chemical substances.

Another object of the present invention is to provide a method for recording and storing information regarding structural changes of chemical substances in an expression form that can be processed by a computer.

A further object of the present invention is to provide a method for recording and storing chemical reaction information that integrates information regarding starting materials, product materials, and structural changes between them in a computer-processable representation format. It is something.

That is, the present invention is topologically superimposed in a method of recording and preserving information regarding a chemical reaction that produces at least one product from at least one starting material. Between the structure of the starting material and the structure of the product, (1) bonds between nodes that exist in common in the starting material and the product, (2) bonds between nodes that exist only in the starting material, and (3) A method for recording and storing chemical reaction information is provided, which is characterized in that a chemical reaction is expressed by separately representing the bonds between nodes that exist only in the produced substances.

The present invention also provides 1) a method for recording and storing information regarding a chemical reaction that produces at least one product from at least one starting material, wherein the structure of the starting material and the structure of the product are topologically superimposed; (1) Bonds between nodes that exist in common in the starting material and product material, (
2) Bonds between nodes present only in the starting material, and (
3] Create a structural diagram that expresses the structural change of the substance in the chemical reaction based on bond information in which bonds between nodes that exist only in the product substance are separately represented,
and 2) a method for recording and storing chemical reaction information, characterized by recording and storing chemical reactions in the form of structural diagrams, and 2) recording and storing information regarding chemical reactions that produce at least -. products from at least one starting material. In the method of
(2) Bonds between nodes that exist only in the starting material, and (3) Bonds between nodes that exist only in the product material are each expressed separately based on bond information. Provided is a method for recording and storing chemical reaction information, comprising: creating a bonding table containing information about binding partner nodes to be bonded to and bonds between the nodes; and storing chemical reactions in the form of the bonding table. It is something to do.

According to the method of the present invention, a chemical reaction is basically expressed in a simple expression of a bond between a mate and a node consisting of atoms, atomic groups, etc. Bonds between nodes in a reaction system can be distinguished into three types: bonds that exist only in the starting material, bonds that exist only in the product, and bonds that exist in common to both, so only the chemical reaction itself can be expressed. Instead, it can also be expressed about substances such as starting materials and produced substances that are involved in the reaction. That is, compared to various conventional expression methods, the present invention is an extremely superior method in that it can simultaneously record and store both chemical substance information and chemical reaction information.

Furthermore, by utilizing the uninvented representation method when recording and storing chemical reaction information, the information can be easily processed by a computer without requiring a large storage capacity. Furthermore, since it is possible to easily record the chemical reactions on the recording medium, it becomes easy to accumulate and manage this information. In addition, based on registered chemical reaction information, etc., information on chemical reactions and chemical substances related to reactions can be searched efficiently in a short time, so engineers can use information for their individual research. It is possible to shorten the time required for collection, investigation, etc., and increase the density of information obtained, making it possible to proceed with research efficiently. In addition, we also conduct structural analysis and molecular design of chemical substances (molecular model B), which are a must for engineers involved in drug manufacturing, etc.
, organic synthesis route design (heuristic analysis)
sis of organic 5yntheSis
) and other applied fields.

Then, chemical reaction information can be recorded and stored (registered) in a computer as a two-dimensional or three-dimensional structural diagram and/or a bonding table using the - expression method. In the present invention, the structural diagram refers to a diagram (this is called an f-imaginary transition structure J) that represents the structural change of a substance involved in a chemical reaction using the L-notation representation method, and is a diagram that represents the structural change of a substance involved in a chemical reaction. Based on three-dimensional structural diagrams, chemical reactions can be represented in a form that is visually familiar to engineers and easy to understand. In addition, the bond table is a simple and clear structure consisting of combinations of node types, partner nodes that connect to the nodes, and the types of connections between these nodes, and it allows chemical reactions to occur without requiring a large capacity. Information can be stored and stored on the Q medium.

In both of the registration forms of these structure diagrams and bond tables, the bonds connecting each node are expressed in relation to the starting materials and produced substances, so the structure 1χ and the bond table describe not only chemical reactions but also substances involved in the reactions. It also contains comprehensive information. Therefore, using registered structure diagrams and/or bonding tables, chemical substances and chemical reactions can be calculated in original format.
'J1 position can be searched and matched.

Furthermore, in the present invention, if the connection table also includes information about the spatial coordinates of each 7-dot, it is possible to arbitrarily convert between the L structure garden and the connection table. , chemical reactions can be displayed and recorded in either form.

In addition to the advantages mentioned above, for example, the bonds between each mate can be represented by a pair of numbers (a, b) [where a is an integer representing the bond multiplicity in the starting materials and b is the change in bond multiplicity in the chemical reaction. is an integer representing
Not only individual reactions but also multiple consecutive reactions (multi-step reactions) can be collectively represented in one bond table, and any intermediate reactions and a series of synthetic reactions can be easily displayed. Therefore, by using the record storage method using the structure diagram and/or connection table of the present invention,
Search for substructures of chemical substances and chemical reactions, structure-activity relationships (1 molecule, 2), synthetic route design, automatic structure determination of unknown compounds, and reaction mechanisms when complex compounds are reacted under certain conditions. After reaction, the reaction product I'411 (m
Echanistic evaluation of o
rganic reaction) etc. can be carried out in a short time within a practical range of one minute.

[Structure of the Invention] In the present invention, structural changes of chemical substances in chemical reactions include bonds that exist only in the starting material and bonds that exist only in the product when the structure of the starting material and the structure of the product are topologically superimposed. It is expressed by distinguishing into three types: bonds that exist in common to both, and bonds that exist in common to both.

The method for recording and storing chemical reaction information of the present invention will be explained by taking as an example a reaction in which ethyl acetate is hydrolyzed with hydrochloric acid.

This chemical reaction is CH3COOCH2CH3+ H20+ HCD-→C
It is represented by H,COOH+CH,CH,,O)l+HCQ (reaction formula j). All starting materials involved in the reaction (fiber)
The nodes are numbered 1llll-1 as follows.

Thick-system (6) CH CoC-0CH2-CHo + H-0-H+ H-0 Next, the yarn (starting material group) and production system (product material group) expressed by the usual structural formula. If you superimpose them topologically, that is, with the same phase.

(8) (II) A structure expressed by (II) can be obtained. Here, l) symbol - is
11) The symbol X'j← represents a bond that exists only in the starting material, and 111) The symbol... represents a bond that exists 1° and 1'1 in common in the starting material and the product material. represents a bond that exists only in

In the present invention, 5F, structure 1 is converted into an imaginary transition structure (im
aginary transition 5truct
ures, hereafter abbreviated as ITS). In other words, an imaginary transition structure (ITS) is a two-dimensional or A two-dimensional structure.

The product system obtained as a result of the hydrolysis reaction is represented by the following structural formula corresponding to the mate number of the yarn.

Generation system (6) C) I, -C-0-H + )l-0-CH,, -1:H3+ H-CΩ(1
0) (3) (4) (5) (U cl
l) In the present invention, the term "topological superposition" refers to the structure of the starting material. This refers to matching nodes with nodes that appear in the structures of generated substances and combining these structures.

In the present invention, all atoms contained in the filament and the production system may be used as nodes of substances involved in chemical reactions, or methyl groups [E Node (, 1),
(5) ], methylene group [above node (4)]
It may also be an atomic group such as a functional group such as. Further, when expressing a chemical reaction, it is also possible to partially omit some nodes appearing in the yarn and the production system, and this is also included in the present invention.

In the imaginary transition structure (ITS) according to the present invention.

The distinction between the three types of bonds is not limited to the symbols i) to 1ii) above; for example, the numbers (
1, 2, 3) The display using simple letters in 4 or the color division (black, red, green) can be done in any way as long as the user can judge it with their five senses and it is possible to process it with combinations of characters. This may be done using other means.

Hereinafter, in the present invention, ]) A bond (symbol -) common to the starting material and the product is called a colorless bond, and a bond that exists only in the starting material (symbol 1) is called an outgoing bond. 1ii) The bond (symbol...) that exists only in the generated substance is called the "inbound bond J," and the outbound bond and inbound bond are collectively called the r-colored bond.

Specifically, Table 1 summarizes the types of bonds that appear in the imaginary transition structure of the present invention. Note that in Table 1, the horizontal numbers mean indicators of the inflow and outflow of bonds.

In the lower margin of Table 1, for example, the bond represented by the symbol r...'' is a single 1n-bond and can be represented by a pair of numbers (0+1).

Here, 0 means that there is no bond in the original system before the reaction, and +1 means that a single bond is present in the product system after the reaction. Similarly, bonds represented by "-" are single out-bonds.
) It is expressed as (1-1) and means that a single bond exists in the original system before the reaction, but the single bond disappears in the product system after the reaction. Furthermore, the bond represented by (2-1) is an outstanding double bond.
d singly cleaved) and f-4-
”.

In this way, the type of bond is also a pair of numbers = (a, b)
[where a is an integer representing the bond multiplicity in the starting material, and b is an integer representing the change in bond multiplicity in the chemical reaction], in which case the bond multiplicity is double However, it can be written concisely. Note that in the notation (a, b), the comma (1) may be omitted. Also, this notation does not require much storage capacity and can be directly processed by a computer, so it is easy to understand chemical reactions. Particularly suitable for record keeping.

Next, each chemical reaction is recorded and stored (registered) using a method of expression that focuses on the bonds between double nodes, for example, by the method described below.

Records of chemical reactions are stored in the form of the above-mentioned imaginary transition structure, bond table, or a combination thereof.

First, in the above hydrolysis reaction of ethyl acetate with hydrochloric acid, the types of nodes (1) to (11) and the bonds between each node are related to bonds that are distinguished as colorless or colored bonds and out or in bonds. Based on the input information, the structure (
ITS) Create a two-dimensional imaginary transition structure as shown in 1. Of course, it is also possible to create a three-dimensional imaginary transition structure. Therefore, this connection information must include information (two-dimensional or three-dimensional coordinates) regarding the relative spatial arrangement of each node.

Each chemical reaction is then registered in the computer in the form of the resulting two-dimensional or three-dimensional imaginary transition structure (figure). This registered form is very superior in that it is in the form of a structural formula or three-dimensional structural diagram that can be visually understood and judged immediately by those who wish to use the chemical reaction information.

For example, from this registered imaginary transition structure, the structure of the starting material can be obtained by deleting only the incoming bonds (making them non-bonded), and the structure of the product material can be obtained by deleting only the outgoing bonds. In other words, the imaginary transition structure according to the present invention includes not only chemical reaction information but also chemical substance information, and this registered form can be used to perform not only reaction searches but also compound structure searches. .

In addition, in the above ITSI, if only the colorless bonds are deleted, the structure [(2) -(
3) +(10)-(11)+(8)-(7) +(
2) J can be obtained and this can be converted into react
ion string ). Note that - and + here mean outgoing coupling and incoming coupling, respectively. The reaction component can be extracted as a form specific to each reaction type, and in this case, it is an expression of IM in the hydrolysis reaction of an ester. That is, using the registered imaginary transition structure, it is possible to extract only reaction paths that are structural expressions unique to individual reaction types, and reaction searches can be further facilitated. In addition, the ring structures involved in the reaction (
It is also possible to extract only open or closed rings.

Alternatively, in the hydrolysis reaction of ethyl acetate with stone-shaped hydrochloric acid, the types of nodes (1) to (11) and the bonds between each node are distinguished as colorless or colored bonds and out or in bonds. Based on the input information about each node, a connection table (conne
ction table).

The resulting combination table is shown in Table 2. Note that the connection table also includes information regarding the two-dimensional coordinates (xy coordinates) of each node.

As shown in Table 2, the bond table shows the hydrolysis reaction, the fibers involved (ethyl acetate, water, hydrochloric acid) and the production system (acetic acid,
For ethanol, hydrochloric acid), all nodes, their two-dimensional coordinates (with node (1) as the origin), all nodes connected to each node, and the types of connections between these nodes are listed in order of node number. This is a list.

The coupling table can also be created based on the imaginary transition structure obtained above. Alternatively, a connection table can be created directly from information input in the form of an imaginary transition structure.

The individual chemical reactions are then registered in the computer in the form of a bond table. This registration format is excellent in that it does not require a large storage capacity and can be directly processed by a computer. Note that it is of course possible to register a combination of a bond table and an imaginary transition structure, which is preferred in the present invention.

The connection table may also include input information regarding the spatial coordinates of each node, etc., as described above. Furthermore, the imaginary transition structure and/or bond table may include information regarding the charge and stereochemistry of each node, various physical property values and spectral information of the chemical substances involved in the reaction, and enthalpy, temperature, time, etc. of the reaction, if desired. Information regarding the catalyst used, atmosphere, reaction phase, reaction yield, blackness of by-products, etc. may be recorded, and the imaginary transition structure or bond table registered in the computer may contain this additional information. In such cases, the imaginary transition structure or bond table can be widely used as a database in chemical substance structure search systems, chemical reaction search systems, organic synthesis design systems, etc.

When registering the above imaginary transition structure and/or bond table in a computer, a reaction number may be assigned to each imaginary transition structure and/or bond table in order to facilitate the accumulation, management, and retrieval of chemical reaction information. Good, or again.
A reaction name may be registered for each imaginary transition structure and/or bond table.

Based on the registered bond table, it is possible to display starting materials, produced materials, reaction formulas, etc., and it is also possible to extract reaction results and rings involved in the reaction, just as in the case of imaginary transition structures. It is.

Furthermore, by performing appropriate arithmetic processing on the bonds represented by combinations of numbers (a, b), it is possible to integrate reactions spanning multiple stages and display them as a - bond table. That is, it is possible to simply display not only individual reactions but also the entire complex reactions such as those in the synthesis of organic compounds, or to extract and display only a part of the reactions.

Therefore, this registered bond table can be used in a wide range of fields in which computers are used in chemistry, such as molecular design focusing on specific properties of substances, determination of synthetic routes for organic compounds, and automatic structure determination of unknown compounds. It can be used as a feeling.

Conversely, it is also possible to create an imaginary transition structure based on the registered bond table, and in the various search systems mentioned above, it is possible to arbitrarily convert between the bond table and the imaginary transition structure for chemical reactions. can. This makes it possible to perform various searches even more easily, and it is possible to increase the versatility and usability of the search system.

The imaginary transition structure and/or the connection table may be registered in the computer by storing it in the above-mentioned tt device in the computer, or by storing it in a suitable recording medium (
The data may be recorded and saved via a magnetic disk, optical disk, magnetic tape, etc.).

The registered imaginary transition structure and/or bond table can be recorded on various recording materials such as plain paper using a suitable recording head, or displayed on a color cathode ray tube connected to a computer or electronic equipment.

The method for recording and storing chemical reaction information according to the present invention will be further explained below using another embodiment.

[Example 1] Reaction of adding n-butyllithium to acetone This chemical reaction is as follows: H3 → CH3CCH2CH2CH2CH3 OH (Reaction formula 2) % Formula % The imaginary transition structure of the reaction can be expressed as follows.

H(8) (10) (I
TS 2) We also created a bond table corresponding to this imaginary transition structure. The resulting connection table is shown in Table 3. Note that the connection table also includes information regarding the two-dimensional coordinates (xy coordinates) of each node.

[Example 2] Acylation reaction by Friedel-Krach reaction This chemical reaction consists of CH, CH.

CHff CH3 It is expressed as

The imaginary transition structure of the reaction can be expressed as follows.

Below is the margin OHy (12) (10) Also, a bond table corresponding to this imaginary transition structure was created. The resulting combination table is shown in Table 4. Note that the connection table also includes information regarding the two-dimensional coordinates (xy coordinates) of each node.

1, ゛) Bottom white [Example 3] Beckmann rearrangement This chemical reaction is (Reaction formula 4) %formula% The imaginary transition structure of the reaction can be expressed as follows.

We also created a bond table corresponding to this imaginary transition structure. The resulting connection table is shown in Table 5. Note that the connection table also includes information regarding the two-dimensional coordinates (xy coordinates) of each node.

[Example 4] Methylation reaction of cycloheptanone This chemical reaction consists of a series of A-C reactions: [Aco[B] “C” (Reaction formula 5) % formula % (1) The transition structure can be expressed as follows.

CH (11) 1 We also created a bond table corresponding to this imaginary transition structure. The resulting combination table is shown in Table 6. Note that the connection table also includes information regarding the two-dimensional coordinates (xy coordinates) of each node.
, Nru.

', -:';7': White (2) The imaginary transition structure of the B-stage reaction cannot be expressed as below. CHHz (11> Book (8) 0 (15) ■ (18) 1 〆゛・ (5) C-1: (4) In addition, a bonding table corresponding to this imaginary transition structure was created.The resulting bonding table is shown in Table 7.The bonding table is one-dimensional for each node. It also includes information regarding coordinates (xy coordinates).

Side, bottom margin (3) The imaginary transition structure of the C-stage reaction can be expressed as follows.

(5) CC (4) In addition, a bond table corresponding to this imaginary transition structure was created. The resulting combination table is shown in Table 8. Note that the connection table also includes information regarding the two-dimensional coordinates (xy coordinates) of each 7-dot.

The imaginary transition structure that summarizes the reactions in the A and B stages, that is, the reaction consisting of [A] [B] (reaction formula 5''), can be expressed as F below.

We also created a bond table corresponding to this imaginary transition structure. The resulting combination table is shown in Table 9. Note that the connection table also includes information regarding the two-dimensional coordinates (xy coordinates) of each mate.

Below is the blank space (5) A, B and C stage reactions, i.e. [A]
[B1 [C] The imaginary transition structure summarizing the reaction consisting of (reaction formula 5') can be expressed as follows.

We also created a bond table corresponding to this imaginary transition structure. The resulting combination table is shown in Table 10. Note that the connection table also includes information regarding the two-dimensional coordinates (xy coordinates) of each node.

La F sequel? rlj New Year's Day) November 1, 1985■ (Japanese 60th year Patent Application No. 177345 2, Name of invention Method for recording and preserving chemical reaction information 3, Relationship with supplementary IE case Patent applicant name (520) Fuji Photo Film Co., Ltd. 4, Agent address: Mitsuya Yotsuya Building 8, 2-14 Yotsuya, Shinjuku-ku, Tokyo
Level 6: Number of inventions increased by amendment None 7: Subject of amendment Column 8 of "Detailed Description of the Invention" in the specification, Contents of the amendment As per the attached sheet - ・In the "Detailed Description of the Invention" of the description Please correct the fields as below.

Note (1) The structural formula (Structure l) on page 15 is corrected as follows.

(8) (II) (2) The product substance of (reaction formula 3) on page 31 is corrected as follows.

Before correction After correction Seventh

Claims (1)

[Claims] 1. A method for recording and storing information regarding a chemical reaction that produces at least one product from at least one starting material, wherein the structure of the starting material and the structure of the product are topologically superimposed. (1) Bonds between nodes that exist in common in the starting material and product material, (
2) Bonds between nodes present only in the starting material, and (
3) A method for recording and storing chemical reaction information, characterized in that a chemical reaction is expressed by separately representing the bonds between nodes that exist only in the produced substances. 2. The method for recording and storing chemical reaction information according to claim 1, wherein the bond nodes present in the starting material and/or the product material are atoms or atomic groups. 3. A method for recording and storing chemical reaction information according to claim 1, characterized in that the bonds present in the starting material and/or the product material are distinguished by letters, symbols, colors, or a combination thereof. . 4. The bonds present in the starting material and/or product are expressed by a pair of numbers (a, b) [where a is an integer representing the bond multiplicity in the starting material, and b is the bond multiplicity in the chemical reaction. 4. The method for recording and storing chemical reaction information according to claim 3, wherein the chemical reaction information is expressed in distinction by an integer representing a change. 5. A method for recording and storing information regarding a chemical reaction resulting from at least one starting material to at least one product, wherein (1 ) bonds between nodes that exist in common in the starting material and the product, (
2) Bonds between nodes present only in the starting material, and (
3) Create a structural diagram that expresses the structural change of the substance in the chemical reaction based on bond information in which bonds between nodes that exist only in the product substance are separately represented,
And a method for recording and storing chemical reaction information, characterized by recording and storing chemical reactions in the form of a structural diagram. 6. The method for recording and storing chemical reaction information according to claim 5, wherein a chemical reaction name is attached to the structural diagram. 7. A method for recording and storing information regarding a chemical reaction resulting from at least one starting material to at least one product, wherein (1 ) bonds between nodes that exist in common in the starting material and the product, (
2) Bonds between nodes present only in the starting material, and (
3) A bond that includes information regarding each node, a bonding partner node that is bonded to the node, and the bond between the nodes, based on bond information in which bonds between nodes that exist only in the generated substance are individually expressed. A method for recording and storing chemical reaction information, which comprises creating a table and recording and storing chemical reactions in the form of a combination table. 8. The method for recording and storing chemical reaction information according to claim 7, wherein the connection table includes information regarding two-dimensional or three-dimensional coordinates of each node. 9. The method for recording and storing chemical reaction information according to claim 7, wherein a chemical reaction name is attached to the bond table. 10. The method for recording and storing chemical reaction information according to claim 7, characterized in that the chemical reaction is recorded and stored in the form of a bond table and a structural diagram representing a structural change of a substance in a chemical reaction.