JPH07258566A - Coumarin derivative and photopolymer-sensitizing colorant - Google Patents

Abstract

PURPOSE:To obtain a photopolymer-sensitizing colorant which enables high-speed scanning and recording with a visible laser and has excellent characteristics by using a coumarin deriv. as the colorant. CONSTITUTION:This photopolymer-sensitizing colorant comprises a new coumarin deriv. represented by formula l or II [wherein R1 and R2 are each Hor 1-3C alkyl; R3 is optionally branched alkyl, alkyl having an O atom in the carbon chain, halogen, hydroxyl, cyclohexyl, or phenyl-substd. alkyl; and X is a hetrocyclic group having the total number of carbon atoms and heteroatoms of 5-13 or -CO-Y (wherein Y is optionally substd. 1-6C alkyl, alkoxy, optionally substd. phenyl, etc.)]. This photopolymer-sensitizing colorant enables high-speed scanning and recording with a visible laser (e.g. an argon ion laser) and is useful as a sensitizing colorant for a presensitized plate for laser direct processing, a dry film resist. etc. The deriv. is useful as an org. fluorescent material or an org. EL material.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a novel coumarin derivative and a sensitizing dye for photopolymers comprising such a derivative.

[0002]

2. Description of the Related Art Photopolymer compositions are materials that exhibit changes in physical properties in light-irradiated and non-irradiated areas when they are exposed to light energy. They include printing, microfabrication of VLSI, printed circuit formation, UV-curable paints, inks, holograms. It has been put to practical use in a wide range of fields such as recording, and its use is expanding more and more.
This composition is basically composed of a photopolymerization initiator, a photopolymerizable compound and a binder resin, and usually has a spectral sensitivity in the ultraviolet region, and it has a g-line, an i-line of a mercury lamp and a high-power argon laser. An image is recorded using an ultraviolet oscillation line or the like. In recent years, the development of a technique for recording an image using visible laser light instead of ultraviolet light has been actively pursued, and the use of a sensitizing dye is an indispensable technical element in order to give the recording light spectral sensitivity. Has become. The characteristics of the sensitizing dye include (1) excellent solubility in a solvent, (2) large absorption coefficient at the wavelength of recording light, and (3) good sensitivity of the photosensitive wavelength to the wavelength of recording light. It is required that they agree with each other, (4) high sensitivity, (5) good storage stability, and (6) good compatibility with other components. The photopolymer composition is basically composed of a binder polymer, a polyfunctional monomer, a polymerization initiator and a sensitizing dye. There are a great many kinds of each component other than the dye, and the product composition is prepared in various combinations according to the use and the product grade and is used. Therefore, in order to prepare a composition having desired properties, a method is used in which other components are fixed and a dye suitable for this is selectively used. A versatile dye having various properties capable of responding to a composition composed of such various kinds of combinations has not been found so far, and various kinds of useful sensitizing dyes are needed, and development thereof is desired. Has been done. To date, many types of sensitizing dyes for photopolymers have been proposed. For example, JP-A-54-151024 discloses a merocyanine dye, 58
-29803 describes cyanine dyes, 59-56403 describes stilbene derivatives, 63-23901 describes coumarin compounds, and 64-33104 describes methylene blue derivatives. In reality, it is difficult to find a dye having all of the above-mentioned required properties among these known dyes.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the technical field of image recording by a visible laser using a photopolymerizable composition, various characteristics excellent in practicality are required due to the necessity of high-speed scanning exposure recording and low-power laser recording. A sensitizing dye provided is required. However, the molecular structure of the sensitizing dye, the interaction between each component, and the various properties based on it have not been clarified at present, and the search for the dye is often difficult due to trial and error based on experience. However, it is not easy. As a result of earnest studies, the present inventor has synthesized coumarin derivatives having a novel structure, and found that these derivatives have excellent properties as sensitizing dyes for photopolymers.

[0004]

The present invention provides a novel coumarin derivative represented by the following general formula (1) or (2) and a sensitizing dye for a photopolymer comprising the derivative.

[Chemical 1]

[Chemical 2] In the above formula, R ₁ and R ₂ each independently represent a hydrogen atom or a C _{1 to} C ₃ alkyl group. R ₃ represents an alkyl group which may be branched, an alkyl group having an oxygen atom in the carbon chain, or an alkyl group substituted with a halogen, a hydroxy group, a cyclohexyl group or a phenyl group. X represents a heterocyclic group in which the total number of carbon and hetero atoms is 5 to 13 or represents -CO-Y. Here, Y is a C ₁ -C ₆ substituted or unsubstituted alkyl group, an alkoxy group, a substituted or unsubstituted phenyl group, an arylalkenyl group represented by the general formula (3).

[Chemical 3] (In the formula, R ₄ is a hydrogen atom, a C ₁ -C ₄ alkyl group, C _4
1 -C ₄ alkoxy group, a hydroxy group or a halogen. R ₅ represents hydrogen, an alkyl group having an oxygen atom in the carbon chain, or an amino group substituted at the 4-position represented by —NR ₆ R ₇ . Here, R ₆ and R ₇ are each independently a straight-chain or side-chain alkyl group which may be substituted with a halogen, a hydroxy group, an alkylcarbonyloxy group, a phenylcarbonyloxy group or a phenyl group; a substituted or unsubstituted phenyl group Or represents an alkyl group having an oxygen atom in the carbon chain. Further, R ₆ and R ₇ may be combined to form a nitrogen-containing 5-membered or 6-membered ring, and either or both R ₆ and R ₇ are adjacent to the carbon to which the nitrogen atom is bonded. May form a 6-membered ring in cooperation with the carbon of n represents an integer of 1 or 2. ) Or a 3′-coumarinyl group represented by the general formula (4)

[Chemical 4] (In the formula, R ₈ represents hydrogen or an alkoxy group, R ₉ represents hydrogen or an amino group substituted at the 7-position represented by —NR ₁₀ R _11. Here, R ₁₀ and R ₁₁ may be branched. Represents a good alkyl group or an alkyl group having an oxygen atom in the carbon chain, and R ₁₀ and / or R ₁₁ may form a 6-membered ring in cooperation with the carbon next to the carbon to which the nitrogen atom is bonded. Good.) In the above formula, specific examples of R ₁ and R ₂ include a hydrogen atom and an alkyl group selected from methyl, ethyl, propyl and isopropyl. Specific examples of R ₃ include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-.
An optionally branched alkyl group such as butyl, pentyl, hexyl, heptyl, octyl, decyl, octadecyl;
2-ethoxyethyl, 2-butoxyethyl, 2- (2-
An alkyl group having an oxygen atom in the carbon chain such as (ethoxy) ethoxyethyl, 3-methyl-3-methoxypropyl; 2-chloroethyl, 3-chloropropyl, 4-chlorobutyl, 1-bromohexyl, 1-bromoheptyl, etc. Halogen-substituted alkyl group; cyclohexylmethyl,
Alkyl group substituted with a cyclohexyl group such as 4-butylcyclohexylmethyl, 4-ethylcyclohexylmethyl, 4-pentylcyclohexylmethyl; benzyl, 4-methylbenzyl, 4-methoxybenzyl, 4-
Examples thereof include an alkyl group substituted with a phenyl group such as chlorobenzyl, 3-methylbenzyl and 2-phenylethyl. Specific examples of the heterocyclic group for X include 2-benzothiazolyl, 6-methyl-benzothiazolyl, 5-methoxy-2-benzothiazolyl, 5,6-methylenedioxy-2-benzothiazolyl, 6-chloro-2-benzothiazolyl, 5, 6-dimethyl-2-benzothiazolyl,
2-imidazolyl, 2-benzimidazolyl, 2-N-
Methyl-benzimidazolyl, 2-benzoxazolyl, 5-phenylbenzoxazolyl, 5,6-diphenyl-2-oxazolyl, 2- (4,5-benzo) benzothiazolyl, 2- (6,7-benzo) Benzothiazolyl, 2- (6,7-benzo) benzoxazolyl, 5-
Phenyl-2- (1,3,4-thiadiazolyl), 5-
Phenyl-2- (1,3,4-oxadiazolyl), 2
-Heterocyclic groups such as benzoselenazolyl, 2-quinoxalyl and 2-N-ethylquinoxalinyl. or,
Specific examples of Y include substituted or unsubstituted alkyl groups having 1 to 6 carbon atoms such as methyl, ethyl, propyl, hexyl, ethoxycarbonylmethyl, butoxycarbonylmethyl; methoxy, ethoxy, propoxy, butoxy, isopropoxy, phenylmethoxy. An alkoxy group such as; a substituted or unsubstituted phenyl group such as phenyl, 4-methylphenyl, 4-methoxyphenyl, and cyanophenyl; an arylalkenyl group represented by the general formula (3)

[Chemical 3] (The symbols are the same as above); 3'-represented by the general formula (4)
Coumarinyl group

[Chemical 4] (The symbols are the same as above). Specific examples of the arylalkenyl group represented by the general formula (3) include 4-dimethylaminostyryl, 4-diethylamino-2-methylstyryl, 4-diethylamino-2-chlorostyryl,
4-dimethylamino-2-methoxystyryl, 4-diethylamino-2-hydroxystyryl, 4-bis (2-
Hydroxyethyl) aminostyryl, 4-bis (2-chloroethyl) aminostyryl, 4-bis (2-methylcarbonyloxyethyl) aminostyryl, 4-bis (2
-Benzoyloxyethyl) aminostyryl, 4-diisopropylaminostyryl, 4-dioctylaminostyryl, 4-didodecylaminostyryl, 4-bis (2-
Methoxyethyl) aminostyryl, 4-bis (2-ethoxyethyl) aminostyryl, 4- (N-butyl) ethylaminostyryl, 3,4-dimethoxystyryl, 3-
Methoxy-4- (2-methoxy) ethoxystyryl, 4
-Diphenylaminostyryl, 4-bis (4-methylphenyl) aminostyryl, 4-bis (4-methoxyphenyl) aminostyryl, 4-pyrrolidinostyryl, 4-
Morpholinostyryl, 4- (N-ethylpiperazino) styryl, 4- (4-dimethylaminophenyl) butadienyl, 2- (9-eurolidino) ethenyl, 2- [9-
(1,1,7,7-Tetramethyleurolidino)] ethenyl, 2- (8-methyl-9-eurolidino) ethenyl, 2
-[8-hydroxy-9- (1,1,7,7-tetramethyleurolidino)] ethenyl, 2- [6- [1,2,
3,4-tetrahydro-2,2,4,7-tetramethyl-N- (2-butoxyethyl)] quinolyl] ethenyl,
2- [6- (1,2,3,4-tetrahydro-2,2,
4,7-Tetramethyl-N-butyl) quinolyl] ethenyl, 2- [6- (1,2,3,4-tetrahydro-N-
Heptyl) quinolyl] ethenyl and the like. Further, specific examples of the 3′-coumarinyl group represented by the general formula (4) include 3- (7-diethylamino) coumarinyl and 3- (7
-Dibutylamino) coumarinyl, 3- [7bis (ethoxyethyl) amino] coumarinyl, 3- [7- (N-ethyl-N-isobutyl) amino] coumarinyl, 3-coumarinyl, 3- (8-ethoxy) coumarinyl, Formula (5)-
The group represented by (8) may be mentioned.

[Chemical 5]

[Chemical 6]

[Chemical 7]

[Chemical 8]

As the photopolymerization initiator used in combination with the sensitizing dye of the present invention, various organic peroxides, triazine compounds represented by 2,4,6-trichloromethyl-s-triazine, benzoin alkyl ethers, and bisimidazoles. ,
Examples thereof include iron-allene chain products, N-phenylglycine and diphenyliodonium salts. Also, a multi-component initiator obtained by combining these several kinds may be used. As an example of the organic peroxide, as the peroxy ester, di-t-
Butyldiperoxyisophthalate 3,3'4,4 '
-Tetrakis (t-butyldioxycarbonyl) benzophenone, 2,5-as dialkyl peroxide
Dimethyl-2,5-bis (t-butyldioxy) -3-
Hexane, di-t-butyl peroxide, and hydroperoxide include 2,5-bis (hydroperoxy)
-2,5-dimethylhexane, t-butyl hydroperoxide, butyl-4 as a peroxyacetal,
4-bis (t-butyldioxy) valerate, 1,1-
Examples of bis (t-butyldioxy) -3,3,5-trimethylcyclohexane include ketone peroxides such as ethylmethylketone peroxide.

The photopolymerizable compound is composed of a photopolymerizable or photocrosslinkable monomer, oligomer, prepolymer or a mixture thereof having at least one ethylenically unsaturated double bond in one molecule. Examples of such compounds include ethyl acrylate, hydroxyethyl acrylate, ethylene glycol dimethacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, polyester methacrylate, polyurethane methacrylate, epoxy methacrylate, etc. The compound used for can be mentioned.

Examples of the binder resin include poly-N-vinylpyrrolidone, polyvinyl acetate, polyvinyl butyral, polyvinylcarbazole, polystyrene, polymethylmethacrylate, polyethylene oxide,
Examples thereof include polybutylmethacrylate, styrene-maleic acid ester, polymethylmethacrylate-methacrylic acid-based resin, poly-N-vinylpyrrolidone-glycidylmethacrylate-based resin, and the like.

The sensitizing dye according to the present invention is used in a proportion of 0.1 to 10 times that of the photopolymerization initiator, and a binder resin is added in a proportion of 0 to several hundred times to the mixture thereof. A polymerizable composition is prepared. If necessary, additives such as a thermal polymerization inhibitor and a plasticizer may be added to this composition.

Next, the present invention will be described in more detail with reference to examples. Specific examples of the sensitizing dye of the present invention include the following dyes.

[Chemical 9]

[Chemical 10]

[Chemical 11]

[Chemical 12]

[Chemical 13]

[Chemical 14]

[Chemical 15]

[Chemical 16]

[Chemical 17]

[Chemical 18]

[Chemical 19]

[Chemical 20]

[Chemical 21]

[Chemical formula 22]

[Chemical formula 23]

[Chemical formula 24]

[Chemical 25]

[Chemical formula 26]

[Chemical 27]

[Chemical 28]

[Chemical 29]

[Chemical 30]

[Chemical 31]

[Chemical 32]

[Chemical 33]

[Chemical 34]

[Chemical 35]

[Chemical 36]

[Chemical 37]

[Chemical 38]

[Chemical Formula 39]

[Chemical 40]

The dye according to the present invention is a dye according to British Patent 86759.
2, it can be manufactured based on the method described in German Patent 1098125, Japanese Patent Publication No. 51-7488, Japanese Patent Laid-Open No. 63-23901 and the like. The production of the dye will be described with reference to reference examples.

[Reference Example 1] Synthesis of dye 1

[Chemical 41] Obtained by a dehydration condensation reaction between 6-formyl-7-hydroxy-N-ethyl-4,4-dimethyl-1,2,3,4-tetrahydroquinoline represented by and cyanoacetamide

[Chemical 42] 3 g of the intermediate represented by and orthoaminothiophenol 1
Dimethylformamide (10 ml) was added to g, and the internal temperature was 110.
Heat at -120 ° C for 6 hours. After the reaction, the solvent is distilled off by a rotary evaporator, and the obtained crude dye is recrystallized from ethyl acetate to obtain a purified product of dye 1. This product has an absorption maximum wavelength of 470 nm and a melting point of 206-
It shows 210 ° C. The aldehyde compound represented by Chemical formula 41 is obtained as follows. 3-N-ethyl aminophenol and _{(CH 3)} is reacted with ₂ C = CHCH 2 Cl to synthesize tertiary amino phenol, which engaged heating condensation in methanesulfonic acid. When the condensate is formylated by the Beilsmeier reaction by a conventional method,

[Chemical 43] A mixture containing the isomer represented by and the aldehyde derivative represented by Chemical formula 41 is obtained. This is separated and purified using a silica gel column. The attribution of the obtained isomer was identified by NMR.

Reference Example 2 Synthesis of Dye 13 Obtained by reacting the aldehyde represented by Chemical Formula 41 with ethyl acetoacetate.

[Chemical 44] The acetylated compound represented by the formula (4) and 2.0 g of N, N-diethylaminobenzaldehyde are heated and reacted in 80 ml of alcohol in the presence of piperidine. A purified product of the dye is obtained by purifying the obtained crude dye using a silica gel column. This has a maximum absorption wavelength of 4 in methanol.
92 nm, melting point 182-3 ° C.

[Reference Example 3] Synthesis of dye 11

[Chemical formula 45] By reacting 5.2 g of the aldehyde derivative represented by ## STR6 ## with 1.7 g of dimethyl acetonedicarboxylate in 100 ml of alcohol under heating in the presence of piperidine, the crude dye obtained is purified by a silica gel column to obtain a purified product of the dye. This product has an absorption maximum wavelength of 471 nm and a melting point of 271-5 ° C. in methanol.

Reference Example 4 Synthesis of Dye 12 Obtained by reacting the aldehyde derivative represented by Chemical formula 45 with dimethyl acetonedicarboxylate.

[Chemical formula 46] By heat-reacting 3.8 g of a coumarin intermediate represented by and 2.1 g of 4-N, N-diethylaminosalicylaldehyde in 80 ml of alcohol in the presence of piperidine, the obtained crude dye is purified by a silica gel column. Obtain a purified product of the dye. This product has an absorption maximum wavelength of 466 nm and a melting point of 171-2 ° C. in methanol. Other dyes of the present invention can be synthesized in the same manner as in these Reference Examples.

Next, sensitivity measurement will be described. Photosensitive solution formulation: Binder resin (XL-44) 100 parts Polyfunctional monomer (PETA) 100 parts Organic peroxide (BTTB) 8 parts Sensitizing dye 4 parts Methyl cellosolve 900 parts Grain-finished aluminum plate surface-treated with the above photosensitive solution Was spin coated to form a photosensitive layer. An overcoat layer of polyvinyl alcohol was provided to avoid polymerization inhibition by oxygen. Light from a 3 kW ultra-high pressure mercury lamp is passed through a sharp cut filter (Y-47) and an interference filter (KL-49) into this photosensitive layer to extract light of 490 nm close to the oscillation wavelength of an argon laser, and this light is grayed out. The scale was brought into close contact and irradiated. After that, it was developed with an alkaline developer. The sensitivity is based on the gray scale method,
It was calculated from the number of steps of photo-cured steps. The results are shown in Table 1. All the dyes have high sensitivity of 1 millijoule or less. The abbreviations and the structures of the comparative dyes are as follows. XL-44: acrylic acid-methacrylic acid ester copolymer PETA: pentaerythritol triacrylate BTTB: 3,3 ′, 4,4′-tetra (t-butylperoxycarbonyl) benzophenone

[Chemical 47]

[Chemical 48] The dye used in the present invention is a coumarin-based dye having a novel structure. The nitrogen atom bonded to the 7-position becomes a member of the condensed 6-membered ring and is fixed to the coumarin skeleton. Therefore, the donor property of the nitrogen atom is enhanced, the coumarin dye exhibits a large molecular extinction coefficient, and its absorption deepens. On the other hand the same nitrogen atom to impart functions such as high solubility to the dye molecules by introducing includes the ability to bind a substituent R _3, a specific substituent R _3. Due to such characteristics of the molecular structure, this new coumarin-based dye has a synergistic effect such as an improvement in light absorption characteristics and an improvement in matching with a solvent such as cellosolve-based or ketone-based or a dispersion polymer. From the above, according to the present invention, it is possible to provide a new sensitizing dye for photopolymer which has the required characteristics as a sensitizing dye. In addition, 1-phenyl-3,5-bis (trichloromethyl) at the terminal of R ₃ via an ester bond, an ether bond or an amide bond.
Polymerization initiator molecules such as triazine can be linked, and it is also possible to provide a dye having an initiator in the molecule.

[0013]

INDUSTRIAL APPLICABILITY The present invention provides a sensitizing dye for photopolymers having excellent properties, which enables high-speed scanning recording by a visible laser such as an argon ion laser, a PS plate for laser direct plate making, and a dry film resist. , Is extremely useful as a sensitizing dye for material systems such as digital color proofs, hologram recording materials and photosensitive microcapsules. The coumarin derivative according to the present invention is also useful as an organic fluorescent material or an organic EL material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeo Yasui 566-139 Fujita Nishiki, Okayama City, Okayama Prefecture

Claims (2)

[Claims] 1. A coumarin derivative represented by the following general formula (1) or (2): [Chemical 2] [In the above formula, R ₁ and R ₂ each independently represent a hydrogen atom or a C _{1 to} C ₃ alkyl group. R ₃ represents an alkyl group which may be branched, an alkyl group having an oxygen atom in the carbon chain, or an alkyl group substituted with a halogen, a hydroxy group, a cyclohexyl group or a phenyl group. X represents a heterocyclic group having a total of 5 to 13 carbon and hetero atoms or -CO-Y. Here, Y is a C ₁ -C ₆ substituted or unsubstituted alkyl group, an alkoxy group, a substituted or unsubstituted phenyl group, an arylalkenyl group represented by the general formula (3): (In the formula, R ₄ is a hydrogen atom, a C ₁ -C ₄ alkyl group, C _4
1 -C ₄ alkoxy group, a hydroxy group or a halogen. R ₅ represents hydrogen, an alkyl group having an oxygen atom in the carbon chain, or an amino group substituted at the 4-position represented by —NR ₆ R ₇ . Here, R ₆ and R ₇ are each independently a straight-chain or side-chain alkyl group which may be substituted with a halogen, a hydroxy group, an alkylcarbonyloxy group, a phenylcarbonyloxy group or a phenyl group; a substituted or unsubstituted phenyl group Or represents an alkyl group having an oxygen atom in the carbon chain. R ₆ and R ₇ may be combined to form a nitrogen-containing 5-membered or 6-membered ring, and either or both R ₆ and R ₇ may be combined with the carbon adjacent to the carbon to which the nitrogen atom is bonded. May form a 6-membered ring. n represents 1 or 2. ) Or a 3′-coumarinyl group represented by the general formula (4): (In the formula, R ₈ represents hydrogen or an alkoxy group, R ₉ represents hydrogen or an amino group substituted at the 7-position represented by —NR ₁₀ R _11. Here, R ₁₀ and R ₁₁ may be branched. Represents a good alkyl group or an alkyl group having an oxygen atom in the carbon chain, and R ₁₀ and / or R ₁₁ may form a 6-membered ring in cooperation with the carbon next to the carbon to which the nitrogen atom is bonded. Good.) ]. 2. A sensitizing dye for photopolymer comprising a coumarin derivative represented by the following general formula (1) or (2): [Chemical 2] [In the above formula, R ₁ and R ₂ each independently represent a hydrogen atom or a C _{1 to} C ₃ alkyl group. R ₃ represents an alkyl group which may be branched, an alkyl group having an oxygen atom in the carbon chain, or an alkyl group substituted with a halogen, a hydroxy group, a cyclohexyl group or a phenyl group. X represents a heterocyclic group having a total of 5 to 13 carbon and hetero atoms or -CO-Y. Here, Y is a C ₁ -C ₆ substituted or unsubstituted alkyl group, an alkoxy group, a substituted or unsubstituted phenyl group, an arylalkenyl group represented by the general formula (3): (In the formula, R ₄ is a hydrogen atom, a C ₁ -C ₄ alkyl group, C _4
1 -C ₄ alkoxy group, a hydroxy group or a halogen. R ₅ represents hydrogen, an alkyl group having an oxygen atom in the carbon chain, or an amino group substituted at the 4-position represented by —NR ₆ R ₇ . Here, R ₆ and R ₇ are each independently a straight-chain or side-chain alkyl group which may be substituted with a halogen, a hydroxy group, an alkylcarbonyloxy group, a phenylcarbonyloxy group or a phenyl group; a substituted or unsubstituted phenyl group Or represents an alkyl group having an oxygen atom in the carbon chain. R ₆ and R ₇ may be combined to form a nitrogen-containing 5-membered or 6-membered ring, and either or both R ₆ and R ₇ may be combined with the carbon adjacent to the carbon to which the nitrogen atom is bonded. May form a 6-membered ring. n represents 1 or 2. ) Or a 3′-coumarinyl group represented by the general formula (4): (In the formula, R ₈ represents hydrogen or an alkoxy group, R ₉ represents hydrogen or an amino group substituted at the 7-position represented by —NR ₁₀ R _11. Here, R ₁₀ and R ₁₁ may be branched. Represents a good alkyl group or an alkyl group having an oxygen atom in the carbon chain, and R ₁₀ and / or R ₁₁ may form a 6-membered ring in cooperation with the carbon next to the carbon to which the nitrogen atom is bonded. Good.) ].