JPH0648347B2 - Image forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a method for developing a silver halide photographic light-sensitive material, and in particular, gives a negative image with extremely high contrast, a negative image with high sensitivity and good halftone dot image quality. The present invention relates to a photographic light-sensitive material.

(B) Prior art Addition of a hydrazine compound to a silver halide photographic emulsion or a developing solution is described in US Pat. No. 3,730,727 (developing solution combining ascorbic acid and hydrazine), 3,227,
No. 552 (using hydrazine as an auxiliary developing agent for directly obtaining a positive color image), No. 3,386,831 (containing β-monophenylhydrazide of aliphatic carboxylic acid as a stabilizer of silver halide sensitizer) No. 2,419,975 and Mees, `` The Theory of Photographic Proce
ss ”3rd edition (1966), page 281 and the like.

Among these, in particular, US Pat. No. 2,419,975 discloses the addition of a hydrazine compound to obtain a high-tone negative image.

That is, a hydrazine compound was added to a silver chlorobromide emulsion to obtain 12.8
When developed with a high pH developer such as
It is described that extremely high photographic characteristics of more than 10 can be obtained.

However, a strong alkaline developer having a pH close to 13 is easily oxidized by air, is unstable, and cannot withstand long-term storage and use.
The ultra-high contrast photographic characteristics with a gamma value of more than 10 are extremely useful for the photographic reproduction of continuous tone images by dot image useful for printing plate making or the reproduction of line drawings, whether it is a negative image or a positive image. It is useful.

For such a purpose, conventionally, a silver chlorobromide emulsion having a silver chloride content of more than 50 mol%, preferably 75 mol% was used, and the effective concentration of sulfite ion was extremely low (usually
A method of developing with a hydroquinone developer having a concentration of 0.1 mol / or less was generally used (lith development).

However, in this method, since the sulfite ion in the developer is low, the developer is extremely unstable and cannot be stored for more than 3 days.

Further, since none of these methods requires the use of a silver chlorobromide emulsion having a relatively high silver chloride content, high sensitivity cannot be obtained.

Therefore, there has been a strong demand for obtaining ultrahigh contrast photographic characteristics useful for reproducing halftone images and line drawings by using a high-sensitivity emulsion and a stable developing solution.

To this end, U.S. Pat.Nos. 4,168,977 and 4,224,401.
Issue 4,243,739, Issue 4,269,929, Issue 4,272,614,
No. 4,323,643 and the like disclose silver halide photographic light-sensitive materials which give a very hard negative photographic property by using a stable developing solution, but the acylhydrazine compounds used for them have some drawbacks. I understand.

That is, it is known that these hydrazines generate a nitrogen gas during the development process, and this gas collects in the film to form bubbles, which may impair the photographic image.

Therefore, a compound capable of obtaining extremely hard photographic characteristics even with a small addition amount has been desired in view of reducing the generation of bubbles and simultaneously reducing the cost for producing a light-sensitive material. Further, when development is continued using these hydrazines, countless circular fog (sand fog;
pepper fog) is likely to occur and the image quality is significantly impaired.

Further, conventional hydrazines are required in large amounts for sensitizing and hardening, and when it is required that the sensitivity of the photosensitive material is particularly high, other sensitization techniques (for example, chemical sensitization) Enhancing feeling; Enlarging particle size; US Pat. No. 4,27
2,606 or 4,241,164, etc.) is preferably used in combination with a compound that promotes sensitization.
When these sensitizing techniques are used in combination, sensitization with time and fog may generally occur during storage.

Furthermore, when development is performed using conventional hydrazines,
So-called uneven development, which is caused by uneven stirring of the developer, is likely to occur. This development unevenness is remarkable in the developing machine processing, and if the development processing is strengthened in order to eliminate this phenomenon, the above-described sand fog phenomenon occurs.

Therefore, there has been a demand for a compound which does not have the problems of stability over time, development unevenness and sand fog as described above, is effective even when added in a very small amount, and is easy to synthesize.

The present inventors have previously disclosed oxalic acid type hydrazines in Japanese Patent Application No. 61-20700 and Japanese Patent Application No. 61-22458, but compounds according to these inventions are still insufficient. It has been discovered that more effective compounds have been desired.

(C) Object of the Invention The first object of the present invention is to obtain a photographic characteristic of extremely hard negative gradation with a gamma of more than 10 by using a stable developing solution. The object is to provide a silver halide photographic light-sensitive material.

A second object of the present invention is to provide a negative-working silver halide photographic light-sensitive material containing hydrazines which can provide good image quality without problems such as uneven development and sand fog.

Thirdly, the object of the present invention is to provide a negative-type silver halide photographic containing hydrazines capable of imparting desired extremely hard negative tone photographic characteristics with a small addition amount without adversely affecting photographic performance. To provide a light-sensitive material.

Fourthly, the object of the present invention is to improve the processing stability (no development unevenness, sand fog, etc.) and to add a hydrazine compound capable of giving a photographic characteristic of rapid high contrast to the development processing solution to obtain halogen. It is an object of the present invention to provide a method for developing a silver halide photographic light-sensitive material in high contrast.

(D) Structure of the Invention The objects of the present invention have been achieved by developing a silver halide photographic light-sensitive material in the presence of a compound represented by the following general formula (I).

General formula [I] [In the formula, Ar represents an aryl group, and R ₁ represents a hydrogen atom or an alkyl group.

R represents an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an acylamino group, a halogen atom or an alkenyl group.

m represents an integer of 1 or 2, and n represents an integer of 0, 1, 2, or 3.

However, when n = 2 and the substituents R are adjacent to each other,
The substituents R may form a ring. In the general formula [I], the aryl group represented by Ar is
Specifically, it is a phenyl group or a naphthyl group which may have a substituent, and an example of the substituent is an alkyl group,
Aryl group, halogen atom, alkoxy group, aryloxy group, alkenyl group, substituted amino group, acylamino group, sulfonamide group, alkylideneamino group, thiourea group, thioamide group, heterocyclic group, or a combination thereof Can be mentioned.

In the general formula [I], among the groups represented by R ₁ , the alkyl group is preferably an alkyl group having 10 or less carbon atoms, which is a halogen atom, a carboxy group, an alkoxy group, an aryloxy group, a sulfo group. It may have a substituent such as a group, an aryl group, and a substituted amino group.

In the general formula (I), among the groups represented by R, the alkyl group and the alkenyl group are preferably alkyl groups and alkenyl groups having 10 or less carbon atoms, such as a halogen atom, a cyano group, a carboxy group and an alkoxy group. It may have a substituent such as a group, an aryloxy group, a sulfo group, an aryl group and a substituted amino group.

In the general formula [I], the aryl group of the groups represented by R is a phenyl group which may have a substituent or a naphthyl group.

Examples of preferable substituents include an alkyl group, an aryl group, a halogen atom, an alkoxy group, an aryloxy group,
Examples thereof include an alkenyl group, a substituted amino group, and combinations thereof.

In the general formula [I], the alkoxy group among the groups represented by R is preferably an alkoxy group having 1 to 10 carbon atoms, which may be substituted with a halogen atom, an aryl group or the like.

In the general formula [I], among the groups represented by R, the aryloxy group is preferably a monocyclic group and may be substituted with a halogen atom, an alkyl group or the like.

Further, Ar or R of the general formula [I] may have a ballast group incorporated therein which is commonly used in a non-moving photographic additive such as a coupler.

The ballast group is a group having a carbon number of 8 or more and relatively inert to photographic properties, and can be selected from, for example, an alkyl group, an alkoxy group, a phenyl group and a phenoxy group.

Specific examples of the compound represented by the general formula [I] are shown below.

However, the present invention is not limited to the following compounds.

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) The compound of the present invention can be easily synthesized by the synthetic scheme shown below.

[Wherein Ar, R, R ₁ , m, and n are the same as those in the general formula [I],
As defined, X represents a halogen atom. That is, the aminophenols represented by the general formula [II] are reacted with the compound represented by the general formula [III] having a phenoxalyl group in a suitable solvent such as dioxane, benzene or DMF under a basic catalyst such as triethylamine. To obtain the intermediate of the general formula [IV] or the general formula [V], and then to react with the corresponding hydrazine compound (Ar—NHNH ₂ ) to easily obtain the desired compound of the general formula [I]. Can be obtained.

Hereinafter, the synthetic method of the compound of the present invention will be described with reference to specific examples.

<Synthesis Example 1> Synthesis of Exemplified Compound 1 a) Synthesis of Intermediate 4- (Phenoxalylamino) phenol Para-aminophenol 10.9 g and dioxane 200 m.
And 14.7m of triethylamine with stirring at room temperature
Was added.

Furthermore, gradually add 19.4 g of phenoxalyl chloride,
The mixture was stirred at the same temperature for about 1 hour.

After the reaction was completed, the reaction solution was poured into water, the desired product was extracted with ethyl acetate, washed with water, and dried with NaSO ₄ .

After drying the ethyl acetate layer, Na ₂ SO ₄ was removed, and the solvent was evaporated under reduced pressure.

The obtained residue was recrystallized with hydrous DMF.

Yield: 23.6 g Melting point: 309-310 ° C Decomposition b) Synthesis of Exemplified Compound 1 4- (phenoxalylamino) phenol 1 obtained in a)
Ethanol 2 in 2.9 g and phenylhydrazine hydrochloride 7.23 g
After adding 00 m and stirring for a while, triethylamine 6.98 m was added and the mixture was heated under reflux for about 5 hours.

After cooling, the precipitated crystals were collected by filtration and washed with water.

The obtained crude crystals were recrystallized with hydrous dioxane to obtain the desired product.

Yield: 8.75g Melting point: 268.5-270 ° C <Synthesis Example 2> a) Synthesis of intermediate, 2.3-dioxo-1.4-benzoxazine 21.8 g of orthoaminophenol and 400 m of dioxane
After adding and dissolving, 30.7 m of triethylamine was added, and phenoxalyl chloride was added while stirring at room temperature.
40.6 g was added in small portions.

After completion of the addition, the mixture was stirred at the same temperature for about 2 hours, then the reaction solution was poured into water, and the precipitated crystals were collected by filtration and washed with water and ethyl acetate to obtain a target intermediate.

Yield: 15.9g Melting point: 281-282 ° C Decomposition b) Synthesis of Exemplified Compound 4. 4.89 g of 2.3-dioxo-1.4-benzoxazine obtained in a) of Synthesis Example 2, 5.84 g of 1-naphthylhydrazine hydrochloride and 150 m of benzene. In addition, triethylamine (4.18 m) was added with stirring, and the reaction solution was heated under reflux for about 2 hours.

After cooling, the precipitated crystal was collected by filtration and washed with water, and the obtained crystal was recrystallized with hydrous methanol.

Yield: 6.4g Melting point: 247-247.5 ° C <Synthesis Example 3> Synthesis of Exemplified Compound 6 To the intermediate obtained in a) of Synthesis Example 1, 2.57 g of 4- (phenoxalylamino) phenol and 1.75 g of paramethoxyphenylhydrazine hydrochloride, 100 m of ethanol and 1.4 m of triethylamine were added. And refluxed for about 2 hours.

After the reaction, the solution was allowed to cool and crystals were precipitated.

This was collected by filtration, washed with water, and recrystallized with ethanol to obtain the desired product.

Yield: 1.9g Melting point: 232-233 ° C In the light-sensitive material of the present invention, the compound represented by the general formula (I) is preferably contained in the surface latent image type silver halide emulsion layer, but the hydrophilic property adjacent to the surface latent image type silver halide emulsion layer is preferable. It may be contained in the colloid layer.

Such layers include subbing layers, intermediate layers, filter layers, protective layers,
The layer may have any function, such as an antihalation layer, as long as it does not prevent the compound represented by formula (I) from diffusing into the silver halide grains.

Since the content of the compound of the present invention in the layer depends on the characteristics of the silver halide emulsion used, the chemical structure of the compound and the development conditions, the appropriate content may vary over a wide range, but the surface latent image A range of about 1 × 10 ^-6 to 1 × 10 ^-2 moles per mole of silver in a silver halide emulsion of the type is practically useful.

When the hydrazine compound represented by the general formula (I) used in the present invention is mixed in the developing solution, it is from 10 ⁻⁴ to
10 ^-1 mol / ^l is suitable, and more preferably 5-10.
The range of ^{-4 to} 5 x ^-2 mol / is particularly preferable.

The silver halide used in the photosensitive silver halide emulsion layer of the light-sensitive material of the present invention is not particularly limited, and silver chlorobromide, silver chloroiodobromide, silver iodobromide, silver bromide and the like can be used. However, when silver iodobromide or silver chloroiodobromide is used, the content of silver iodide is preferably in the range of 5 mol% or less.

The form, crystal habit, size distribution, etc. of the silver halide grains are not particularly limited, but those having a grain size of 0.7 micron or less are preferable.

A silver halide emulsion is a sulfur compound that reacts with a gold compound such as chloroaurate or gold trichloride, a salt of a noble metal such as rhodium or iridium or a silver salt to form silver sulfide, a stannous salt, The sensitivity can be increased with a reducing substance such as amines without coarsening the particles.

Further, an iron compound such as a salt of a noble metal such as rhodium or iridium or a red blood salt may be allowed to be present during physical ripening or nucleation of silver halide grains.

In particular, the addition of a rhodium salt or a complex salt is preferable because it further promotes the effect of the present invention of achieving photographic characteristics of ultra-high contrast in a short developing time.

In the present invention, the surface latent image type silver halide emulsion refers to an emulsion composed of silver halide grains having a surface sensitivity higher than the internal sensitivity, and this emulsion is preferably defined in U.S. Pat. It has a difference between the surface sensitivity and the internal sensitivity.

The silver halide emulsion is preferably monodisperse, and particularly preferably an emulsion having monodispersity defined in the above-mentioned US Pat. No. 4,224,401.

The photographic emulsion used in the present invention may be spectrally sensitized with methine dyes and the like.

The dyes used include cyanine dyes, merocyanine dyes, complex cyanine dyes, complex merocyanine dyes, holopolar cyanine dyes, hemicyanine dyes, styryl dyes, and hemisonol dyes.

Particularly useful dyes are cyanine dyes, merocyanine dyes,
And a dye belonging to the complex merocyanine dye.

These sensitizing dyes may be used alone or in combination.

A combination of sensitizing dyes is often used especially for the purpose of supersensitization.

A dye that does not itself have a spectral sensitizing effect or a substance that does not substantially absorb visible light together with a sensitizing dye,
A substance exhibiting supersensitization may be included in the emulsion.

As the binder or protective colloid that can be used in the emulsion layer or the intermediate layer of the light-sensitive material of the present invention, it is advantageous to use gelatin, but other hydrophilic colloids can also be used.

For example, gelatin derivatives, graft polymers of gelatin and other polymers, proteins such as albumin and casein: cellulose derivatives such as hydroxyethyl cellulose, carboxymethyl cellulose, cellulose sulfate ester;
Sodium alginate, sugar derivatives such as starch derivatives; polyvinyl alcohol, partial acetals of polyvinyl alcohol, poly-N-vinylpyrrolidone, polyacrylic acid, polymethacrylic acid, polyacrylamide, polyvinylimidazole, polyvinylpyrazole, etc., single or copolymers. A variety of synthetic hydrophilic polymeric substances such as

Examples of gelatin include lime-processed gelatin, acid-processed gelatin, Bull, Soc.Sci.Phot.Japan, NO.16, P30 (1
The enzyme-treated gelatin as described in 966) may be used, or a hydrolyzed product or an enzymatically decomposed product of gelatin may be used.

The photographic emulsion used in the present invention may contain various compounds for the purpose of preventing fog during the production process of the light-sensitive material, during storage or during photographic processing, or for stabilizing photographic performance.

That is, an azole agent, for example, benzothiazolium salt, nitroimidazoles, nitrobenzimidazoles, chlorobenzimidazoles, mercaptothiazoles, mercaptobenzothiazoles, mercaptothiadiazoles, aminotriazoles, benzotriazoles,
Mercaptotetrazoles; mercaptopyrimidines,
Many compounds conventionally known as antifoggants or stabilizers such as mercaptotriazines, thioketo compounds, azaindenes, etc. can be added.

Among these, particularly preferred are benzotriazoles (eg 5-methylbenzotriazole) and nitroindazoles (eg 5-nitroindazole).

These compounds may be contained in the treatment liquid.

The photographic light-sensitive material of the present invention may contain an inorganic or organic hardener in the photographic emulsion layer or other hydrophilic colloid layer.

For example, chromium salts (chrome alum etc.), aldehydes (formaldehyde, glyoxal etc.), N-
A methylol compound, a dioxane derivative (such as 2,3-dihydroxydioxane), an active vinyl compound, an active halogen compound (such as 2,4-dichloro-6-hydroxy-S-triazine), or the like can be used alone or in combination.

The photographic emulsion layer or other hydrophilic colloid layer of the light-sensitive material produced by using the present invention includes a coating aid, an antistatic agent, an improvement in slipperiness, an emulsion dispersion, an adhesion prevention and an improvement in photographic characteristics (for example,
Various surfactants may be included for various purposes such as acceleration of development, hardening, and sensitization.

Non-ionics such as saponins (steroids), alkylene oxide derivatives (polyethylene glycol, polyethylene glycol alkyl ethers, etc.), glycidol derivatives (alkenyl succinic acid polyglycerides, etc.), fatty acid esters of polyhydric alcohols, alkyl esters of sugars, etc. Surfactants; acidic such as carboxy group, sulfo group, phospho group, sulfuric acid ester group, phosphoric acid ester group, such as alkyl carboxylate, alkyl sulfonate, alkyl sulfate, alkyl phosphate, etc. Group-containing anionic surfactants; amphoteric surfactants such as amino acids, aminoalkyl sulfonic acids, aminoalkyl sulfates or phosphoric acid esters; aliphatic or aromatic quaternary ammonium salts, pyridinium, imidazolium, etc. Cationic surfactants such as ring quaternary ammonium salts can be used.

The photographic light-sensitive material used in the present invention includes a photographic emulsion layer and other hydrophilic colloid layers for the purpose of improving dimensional stability,
It may contain a water-insoluble or sparingly soluble synthetic polymer decomposition product.

For example, alkyl (meth) acrylate, alkoxyalkyl (meth) acrylate, glycidyl (meth) acrylate, (meth) acrylamide, vinyl acetate, acrylonitrile, olefin, styrene, etc., alone or in combination, or with these, acrylic acid, methacrylic acid,
A polymer having a monomer component of a combination of α, β-unsaturated dicarboxylic acid, hydroxyalkyl (meth) acrylate, sulfoalkyl (meth) acrylate, styrenesulfonic acid and the like can be used.

To obtain ultrahigh contrast photographic characteristics using the silver halide light-sensitive material of the present invention, conventional lith developers and US Pat.
It is not necessary to use the highly alkaline developing solution close to pH 13 described in the specification No. 5, and a stable developing solution can be used.

That is, the silver halide photographic light-sensitive material of the present invention contains sufficient sulfite ion as a preservative (especially 0.15 mol / or more).
It is possible to use a developer containing it, and a pH of 9.5 or higher,
In particular, a developer of 10.5-12.3 can sufficiently obtain a super-high contrast negative image.

There is no particular limitation on the developing agent that can be used in the method of the present invention, and dihydroxybenzenes, 3-pyrazolidones,
Aminophenols and the like can be used alone or in combination.

Other developers include alkali metal sulfites, carbonates,
Development inhibitors or antifoggants such as pH buffers such as borates and phosphates, bromides, iodides, and organic antifoggants (particularly preferably nitroindazoles or benzotriazoles). Can be included.

Further, if necessary, a water softener, a dissolution aid, a color tone agent, a development accelerator, a surfactant, a defoaming agent, a film hardener, a film silver stain inhibitor (for example, 2-mercaptobenzimidazole sulfonic acid). May be included.

Specific examples of these additives are described in Research Disclosure No. 176, 17643 and the like.

As the fixer, a fixer having a generally used composition can be used.

As a fixing agent, in addition to thiosulfate and thiocyanate,
Organic sulfur compounds known to be effective as a fixing agent can be used.

Further, the fixing solution may contain a water-soluble aluminum salt as a hardening agent.

In the present invention, a method of incorporating a developing agent in a light-sensitive material and processing with an alkaline activator solution may be adopted.

(JP-A-57-129436 and 57-129433)
No. 57-129434, No. 57-129435
No., U.S. Pat. No. 4,323,643).

The treatment temperature is usually selected between 18 ° C and 50 ° C, but 1
The temperature may be lower than 8 ° C or higher than 50 ° C.

It is preferable to use an automatic processor for photographic processing.

In the present invention, even when the total processing time from putting the light-sensitive material in the automatic developing machine until it comes out is set to 60 seconds to 120 seconds, a sufficiently high-hardness negative tone gradation photographic characteristic can be obtained.

(E) Example <Example 1> 97% AgBr, 3% AgI in average particle size 0.25μ
A cubic silver iodobromide emulsion was prepared by the double jet method, washed with water and redissolved by a conventional method, and then chemically sensitized with sodium thiosulfate.

After dividing this silver iodobromide emulsion into 9 pieces, the compounds (2), (6) and (7) of the general formula (I) of the present invention and the comparative compound (A) were added in the amounts shown in Table 1. After addition, it was coated on a polyester film so that the amount of silver was 3.7 g per 1 m ² .

The film sample thus produced was subjected to wedge exposure, and then a developing solution having the composition shown below was used,
Was developed for 1 to 5 minutes.

<Developer> Hydroquinone 30 g 4-Hydroxymethyl-4-methyl-1-phenyl-3-pyrazolidone 0.3 g Sodium sulfite 75 g EDTA.2Na 1.0 g Tripotassium phosphate 80 g Potassium bromide 2.0 g NaOH 13 g 5-Methylbenzotriazole 0.3 g 1-Diethylamino-2,3-dihydroxypropane 17 g Water was added and adjusted to pH 11.5 with potassium hydroxide.

Comparative compound (A) The results are shown in Table I.

As is clear from Table I, the compound of the present invention has a photographic characteristic that is harder to develop even at the development processing of 20 ° C. for 1 minute than the comparative compound (A), and the development is not performed for a long time. You can see that there is no increase in fog even if you go.

Further, the sensitivity change due to the change of the development time is different from the comparative compound (A)
Since it is extremely small compared to the above, it is understood that the stability against development is high.

In addition, when the unexposed part of each sample after development processing was observed, in the sample (NO.2.3) to which the comparative compound (A) was added, obvious sand fog had already occurred at the development time of 3 minutes. Samples containing the compound of the present invention (NO.
In 9), no sand fog was observed.

Example 2 Next, another part of the film sample obtained in Example 1 was used for the halftone dot quality test.

That is, using a 150-line gray contact screen,
Each film sample was exposed through the exposure wedge for sensitometry, and the same developer as before was used at 38 ° C for 30 ° C.
It was developed for 2 seconds and the halftone quality was observed.

The results are shown in Table II.

The halftone dot quality was visually evaluated on a scale of 5, with 5 being the best and 1 being the worst. As the halftone dot plate for plate making, 5 and 4 are practical, and 3 is poor, but they can be used barely and 2 and 1 are practically unusable qualities.

As is clear from Table II, the compounds of the present invention show good halftone dot quality.

Example 3 Another part of the sample of film No. 1 obtained in Example 1 (without addition of a contrast-increasing agent) was subjected to wedge exposure, and then the developer described in Example 1 was applied with the solution of the present invention. Compounds (5), (6),
(12) was added in an amount of 1.5 mmoles per developer.

For comparison, Comparative Compounds (B) and (C) were also added in an amount of 1.5 mmole per developer, and development was carried out at 20 ° C. for 2, 4 and 6 minutes to obtain photographic characteristics.

Comparative compound (B) Comparative compound (C) The results are shown in Table III.

As is clear from Table III, the compound of the present invention has a faster rise in development than the comparative compound (B), and has high photographic characteristics even in the development process at 20 ° C. for 2 minutes.
Moreover, it can be seen that there is no increase in fog even after development for a long time.

Furthermore, these things are the compounds (5), (6),
It is further clarified by comparing (12) with the comparative compound (C).

Claims (1)

[Claims] 1. An image forming method comprising developing a silver halide photographic light-sensitive material in the presence of a compound represented by the following general formula [I]. General formula [I] [In the formula, Ar represents an aryl group, and R ₁ represents a hydrogen atom or an alkyl group. R represents an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an acylamino group, a halogen atom or an alkenyl group. m represents an integer of 1 or 2, and n represents an integer of 0, 1, 2, or 3. However, when n = 2 and the substituents R are adjacent to each other,
The substituents R may form a ring. ]