JPH0577302B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention is a high-density film in which a conductive or semiconductor electrode is placed on a smooth and homogeneous organic insulating (ultra) thin film with a thickness of 10A or more accumulated on a conductive or semiconductor substrate. Regarding molecular LB membrane electrical devices. [Conventional technology] Varistors, thyristors, diodes, photodiodes, light emitting diodes, transistors, and LSIs that integrate them are basically MIM
(Metal/Insulator/Metal: Metal/Insulator/Metal), MIS (Metal/Insulator/Semiconductor:
Metal/Insulator/Semiconductor), MS(Metal/
Semiconductor: Metal/Semiconductor = Schottky element), SIS (Semiconductor/Insulator/
Semiconductor), etc. For MIM, MIS, and MSM devices that require an I layer, the surface of a substrate made of aluminum, beryum, or silicon is usually thinly oxidized to form a metal oxide or SiO ₂ insulating layer, and then a counter electrode is formed. A method of establishing a However, this method cannot be applied to metals or semiconductor substrates other than those mentioned above, and especially when semiconductors other than Si, including compound semiconductors, are used, it can be applied to diodes, photodiodes, light emitting diodes, field effect transistors,
It cannot be applied to MIS type elements, which have a wide range of applications. Therefore, if an organic insulating (ultra)thin film can be used for the I layer, all combinations should be achievable. In this case, the insulating (ultra)thin film used is required to have a thickness of 50A or less, preferably 20A or less, and be smooth and homogeneous. One of the methods for producing smooth, homogeneous, ultra-thin organic films with uniform molecular orientation is the Langmiur-Blodget method (hereinafter referred to as the LB method). In the LB method, organic molecules are preferably dissolved in a dilute solution of an organic solvent that is immiscible with water;
It is spread on a clean horizontal surface, and the gas film that remains after the solvent evaporates is compressed in the plane direction to form a solid film with densely packed molecules.Then, the solid substrate is moved vertically vertically to the horizontal surface. This refers to a method of transferring and accumulating a solid film on the surface of a solid substrate, and the (ultra)thin film formed on the substrate as a result is called an LB film (for example, reference KB
Blodgett, J.Am.Chem.Soc., 55 , 1007 (1935)
). In response, a horizontal adhesion method has been developed in which the substrate is stacked up and down so that it is in horizontal contact with the solid film surface (References K. Fukuda et al., J. Colloid Interface
Sci., 54 , 430 (1976)), and (ultra)thin films on substrates produced by the horizontal deposition method are also now called LB films.
The advantage of LB films is that they can be made from ultra-thin films on the molecular order to cumulative films of arbitrary thickness by repeating lamination, and are smooth and homogeneous films with uniform molecular orientation. Therefore, LB films are expected to be used as materials for various electronics, as will be described later in [Effects of the Invention], and the use of linear fatty acids with carbon atoms of 16 or more, their alkaline earth metal salts, and cadmium salts as LB films has been widely studied. [For example, Kiyonari Fukuda, Hiroo Nakahara (co-author), Chemistry Review 40 “Molecular Assemblies” p82
-104, 1983, and references thereof]. However, the mechanical strength of LB films of these fatty acids or their metal salts is
It has poor heat resistance and cannot be put to practical use. Therefore, either the polymerizable fatty acid is made into an LB film and then subjected to polymerization treatment.
Alternatively, a method has been devised in which the LB film is formed after polymerization on the water surface (reference, same as above), but the post-polymerization method causes severe twitching and crack formation of the film during polymerization, and the above-water polymerization method requires setting of polymerization conditions. difficult,
In addition, it becomes extremely difficult to transfer onto the substrate by both vertical dipping and horizontal adhesion. Therefore, if a polymeric LB film with excellent mechanical strength, heat resistance, etc. becomes possible, it would have an extremely large impact on the industry. In general, flexible linear polymers have a thread-like aggregated state in any dilute solution, and cannot form a gas film state when spread on the water surface.
Not suitable for LB. Exceptionally, polypeptide LB membranes have been reported (References, JHMcAlear et al.
Symposium on VLSI Technology, Digest of
Tech.Papers, 82 (1981)), they are soluble only in special multicomponent solvents such as chloroform/trichloroacetic acid/methanol, and trichloroacetic acid, which is an essential component to maintain solubility, is the metal used as a substrate. It is also not suitable as a material for producing the above-mentioned element. [Object of the Invention] Therefore, the object of the present invention is to provide a polymer LB film electric element having a layer of a polymer LB film of polyfumarate of formula (1) which has excellent mechanical strength, heat resistance, etc., and a method for manufacturing the same. That's true. [Structure of the Invention] The present invention provides a solution of the polyfumarate represented by the general formula (1) in an organic solvent that is immiscible with water at a concentration of 0.1 to 3 mg/ml, and then gently spreading the solution on a clean horizontal surface. The organic solvent is evaporated and the surface pressure is 1dyne/cm.
A monomolecular solid film obtained by forming the following gas film and applying pressure in the horizontal direction to control the surface pressure to 10-30 dyne/cm is deposited on a solid substrate by vertical dipping method or horizontal deposition method. Polymer LB
This invention relates to a polymer LB film electric device having a film layer and a method for manufacturing the same.

embedded image In formula (1), R is a group selected from any of the following (a) to (d). (a) A branched hydrocarbon group having 3 to 30 carbon atoms, with the first branching point inside the third carbon when counted from the fumarate ester, and similarly from one branching point to the next branch. A hydrocarbon group in which the number of carbon atoms from minute to point is 3 or less. (b) Does not contain mobile hydrogen such as primary amide, secondary amide, hydroxy, thiol, etc., and does not contain N, O,
It is a branched hydrocarbon group containing a heteroatom selected from P and S, and the number of constituent atoms excluding hydrogen is 3 to 30, and the first one within 3 constituent atoms when counted from the fumarate ester. A hydrocarbon group that has a branching point and the number of constituent atoms from one branching point to the next branching point is 3 or less. (c) A fluorine-based hydrocarbon group selected from trifluoromethyl, pentafluoroethyl, heptafluoro-n-propyl, or a group in which some or all of the hydrogen atoms in the hydrocarbon group in (a) are replaced with fluorine. . (d) A siloxane hydrocarbon group that does not contain a hydroxy group and has the same number of constituent atoms and branching as in (b). The polyfumarate used in the present invention is prepared by the method developed by Otsu et al.
Makromol.Chem., Rapid Commun., 2725
(1981)), and they are detailed in the reference examples. These polyfumarates have a glass transition temperature Tg
It has a temperature of 200°C or higher (decomposition) and is easily soluble in general-purpose organic solvents such as chloroform, ethylene dichloride, dioxane, tetrahydrofuran, and benzene. When polyfumarate is made into a dilute solution of these organic solvents and spread on the water surface to evaporate the solvent, a gas film state is obtained in which the molecules do not interact with each other. This is because the polyfumarate used in the present invention has a rigid side chain and a rod-like molecular form, so that it does not form a thread-like aggregate. When spreading on the water surface, it is necessary to pay attention to the concentration of the polyfumarate solution and the type of solvent.If a concentrated solution or a solution of a solvent that is miscible with water is used, it tends to become a mere water surface spreading film, and in that case, the molecules of the film Not only is it not possible to control orientation, surface smoothness, homogeneity, etc., but also molecular order e.g.
There is no way to prepare ultra-thin films around 10A. Therefore,
It is necessary to choose a solvent that is immiscible with water, such as chloroform, ethylene dichloride, benzene, etc.
In view of its transpiration rate, chloroform is most preferred. In addition, the concentration of the solution to be developed must be 10 mg/ml or less, preferably 0.1-3 mg/ml.
is within the range of The selection of solvent type and concentration also needs to change slightly depending on the working temperature; the higher the temperature, the higher the boiling point solvent, such as benzene or ethylene dichloride, should be selected, and the solution should be more dilute. However, at normal working temperatures in the range of 10-35°C, the above-mentioned conditions of [chloroform - 10 mg/ml or less] are sufficient. In addition, in the LB film of fatty acids (and their metal salts), its sol-gel transition temperature Tc
(Transition from a solid film to a liquid crystal state film) is low, so it is necessary to work at temperatures below 25°C, but the polymer LB film of the present invention has a Tg of 200°C or higher, so
It has the feature that it can be made into LB even at high temperatures up to 80℃. Therefore, not only is there a wide range of selection of working conditions, but a mixed LB film can also be formed from a mixed solvent with functional molecules that dissolve only at such high temperatures. When surface pressure is applied horizontally to the gas film obtained as described above and maintained at 10-30 dyne/cm, it becomes a solid film. How much surface pressure to set depends on the type of polyfumarate used.The surface pressure-area (FA) isotherm curve is stopped in advance, and the surface pressure is set at the sharp rising part of the FA curve corresponding to the solid film phase. Set. This will be explained in detail with examples. Next, this solid film is transferred to the substrate surface by a vertical dipping method or a horizontal deposition method to form an LB film. In the vertical immersion method,
Since it is accumulated when the substrate is lifted and pushed down, a Y film is formed, and in the horizontal deposition method, it becomes a Z film. However, unlike asymmetric linear molecules such as fatty acids,
This polyfumarate is a rigid, cylindrical linear polymer, and there is no distinction between X, Y, and Z films, and in any case, the LB films are of the same type. In addition, for example, poly(di-
In the case of isopropyl) fumarate, the diameter of the cylinder calculated from the molecular model is estimated to be about 10A, but the thickness per layer calculated from the thickness measurement of the LB film is 10-11A, so this LB film It can be seen that the Langmiur film on the water surface has a molecular orientation state in which the molecules are smooth on the plane but are packed laterally. Normal fatty acids or their metal salts
For LB films, the lower limit of the chain length that can be converted into LB due to Tc and solubility is 16 carbons (less than this, it dissolves in the aqueous phase and forms micelles), and the film thickness is 16.
It is about 20A. However, if the polyfumarate of the present invention is used, a tunneling effect will be produced, and a single layer film of about 10A, which can form the above-mentioned device, can be easily obtained. In the vertical dipping method, the speed of vertical movement of the substrate greatly affects the properties of the LB film formed, and with fatty acids, etc., film defects will increase unless the film is accumulated at a speed of 0.5-1 mm/min or less. However, in the polyfumarate LB according to the present invention, sufficient accumulation is possible even at an extremely high substrate movement speed of 10 mm/min. For example, poly(di-isopropyl) fumarate at 10
When 20 layers were accumulated at a rate of mm/min, a photograph was taken using a differential interference optical microscope at a magnification of 400 times, and the film was enlarged to a magnification of 1000 times and observed, no film defects with a size of at least 0.05 μm or more were observed. On the other hand, the LB film of cadmium arachic acid salt accumulated under the same conditions was 1-5μ
Large membrane defects up to m can be seen everywhere. As described above, the LB film of the present invention can be accumulated if the substrate movement speed is 10 mm/min or less, but from the viewpoint of safety, 5 mm/min or less, preferably 2-3 mm/min considering operability is appropriate. be. In the horizontal deposition method, the substrate movement speed at the moment when the solid film on the water surface contacts the substrate should be controlled to 5 mm/min or less, preferably 1-3 mm/min. In the vertical immersion method, almost all metals, plastics, and ceramics can be used as substrate materials, except for strongly hydrophilic materials such as polyvinyl alcohol and polyacrylamide, and Teflon-based materials. Furthermore, in the horizontal deposition method, it is also possible to laminate on Teflon. however,
Although it is affected by the smoothness of the substrate surface, it is sufficient if the mirror surface has no polishing traces observed with the naked eye. Examples of substrates that are particularly useful and easy to accumulate when forming elements include Al,
Si, Ge, Ni, Fe, Co, Cu, Pt, Au, rare earth metals, metal oxides and metal oxide semiconductors, e.g.
Compound semiconductors such as SiO ₂ , NiO, SnO ₂ , In ₂ O ₃ , indium tin nesa glass (hereinafter abbreviated as ITO nesa), tin oxide nesa glass (hereinafter abbreviated as nesa), such as gallium arsenide, gallium phosphide, indium phosphide, etc. Chalcogens, such as transition metal selenides and sulfides such as zinc selenide and zinc sulfide,
WO ₃ -based chalcogenides, VO ₂ -based chalcogenides, etc.
These include, but are not limited to, polycarbonate, polyethylene terephthalate, polyethylene, and polypropylene. If a conductive or semiconductor electrode is further provided on the LB film on the substrate obtained in this way by an appropriate method such as vacuum evaporation, radio frequency sputtering, ion beam sputtering, molecular beam epitaxy, etc., the present invention can be realized. A polymer LB film electric device, which is the object of the invention, is obtained. [Effects of the invention] The polymer LB membrane electrical element of the present invention has mechanical strength,
Since it uses a 10A order polyfumarate LB film with excellent heat resistance, moisture resistance, light resistance, transparency, and insulation as a layer, it can be applied to all M and S material systems, and has the following properties. used. (1) MIM (Metal/Insulator/Metal) type element,
i.e. barista, thyristor, etc. (2) MIS type devices, i.e. diodes, photodiodes, light emitting diodes (LEDs), etc. (3) SIS (p-Semiconductor/Insulator/n-
Seiconductor) type elements, i.e. diodes,
Photodiode, light emitting diode (LED),
Such. [Description of Examples] Next, the present invention will be described in detail with reference to Examples. Prior to that, the method for producing polyfumarate and the method for producing a polyfumarate LB film used in the present invention will be described using reference examples. Reference Example 1 10g of diisopropyl fumarate was placed in a glass ampoule, and 2,
Add 0.1g of 2′-azobisisobutyronitrile,
Next, the inside of the ampoule was repeatedly purged with nitrogen and degassed, then sealed, and bulk polymerization was carried out at 40℃ for 48 hours. After polymerization, the contents were dissolved in bezene and poured into a large amount of methanol to precipitate the polymer. After separating and thoroughly washing with methanol, dry under reduced pressure to obtain the desired
Poly(diisopropyl fumarate) (PDiPF)
) was obtained. Reference Example 2 Take 10g of ditertiary butyl fumarate in a glass ampoule, add 10ml of benzene, and add 0.2 benzoyl peroxide as a radical polymerization initiator.
Then, the inside of the ampoule was repeatedly purged with nitrogen and degassed, and then sealed, and solution polymerization was carried out at 60° C. for 10 hours. The treatment after polymerization was carried out in the same manner as in Reference Example 1 to obtain the target poly(ditertyabutyl fumarate) (hereinafter abbreviated as PDtBF). Reference Example 3 10g of dicyclohexyl fumarate was placed in a glass ampoule, and 2,
Add 0.1g of 2′-azobisisobutyronitrile,
Next, the inside of the ampoule was repeatedly purged with nitrogen and degassed, and then sealed, and bulk polymerization was carried out at 60°C for 10 hours.
The treatment after polymerization was carried out in the same manner as in Reference Example 1 to obtain the desired poly(dicyclohexyl fumarate) (hereinafter referred to as
PDcHF) was obtained. Reference example 4 Pour pure water to a depth of 2.5 cm into a Teflon trough with an inner area of 20 x 20 cm and a depth of 3 cm, and set the temperature of the entire room to 20°C. Concentration 1mg/ml
Gently spread a chloroform solution of PDiPF on a 150μ water surface and evaporate the solvent. 2.5X5 with No.4 roughness installed so that it is half inserted into the water surface
While detecting the surface pressure by weighing a cm filter paper, a 20 cm long Teflon float placed on the water surface was moved in parallel at a speed of 2 mm/min to narrow the water surface. By observing the surface area and surface pressure, the FA curve shown in Figure 1a was determined. This shows that PDiPF forms a solid film at a surface pressure in the range of 15-25 dyne/cm. Clean ITO Nesa glass with thickness 1.0mm and area 2.5X5cm (surface resistance 10
Ω/cm) was raised and lowered perpendicularly to the water surface at a speed of 2.0 mm/min, and 1 and 20 layers were accumulated by the vertical immersion method while moving the Teflon float so that the surface pressure was always 20 dyne/cm. This LB membrane is 400
Photographs were taken with a differential interference optical microscope at a magnification of 1,000 times and observed after enlarging them to a magnification of about 1,000 times. As a result, no film defects with a size of at least 0.05 μm or more were observed in any case. In addition, the total film thickness determined for the 20-layer LB film based on the surface roughness system is 210A,
From this, the thickness per layer is calculated to be 10.5A. Dry this LB membrane at 100 °C under an argon atmosphere for 12
After a period of time, microscopic observation and film thickness measurement were performed again, but no changes were observed. Example 1 Al was evaporated to a thickness of about 400A as a counter electrode on the LB film of 20 layers of PDiPF of Reference Example 4, and the ITO and Al layers were connected to a conductivity measuring device and conduction was conducted using a DC two-terminal method of 1V. When the temperature was measured, it was found to be less than 10 ^-13 S/cm at 20°C in an argon atmosphere. Furthermore, when we raised the temperature in 5℃ increments and left it at that temperature for 12 hours, we performed the same measurement and found that it was 160℃.
No change was observed in the insulation properties even though the temperature was reached. In addition, ITO/PDiPF− when laminated in one layer
The three-layer structure of LB film/Al corresponds to a thyristor, and the current-voltage (I-
V) Characteristics were shown. Reference example 5 Using the same method as reference example 4, but adding Araquin powder.
Used in place of PDiPF, cadmium chloride was added to the aqueous phase to a concentration of 4mM, and the surface pressure was adjusted.
An LB film was prepared by accumulating 20 layers of cadmium arachinate salt on an ITO substrate at a constant density of 15 dyne/cm. Since it is known that the thickness of one layer of cadmium arachidic acid salt is 28A, the total thickness of this LB film is 220A. As a counter electrode on this LB film
A1 was evaporated to a thickness of about 400A, the ITO and Al layers were connected to a conductivity measuring device, and the conductivity was measured using a DC two-terminal method of 1V.
It was found that it was less than 10 ^-13 S/cm. Furthermore, 5
When the temperature was raised in increments of 12°C and the temperature was left at that temperature for 12 hours, similar measurements were performed, and it was confirmed that dielectric breakdown occurred between 45 and 50°C. Reference example 6 Same as reference example 4, but instead of PDiPF
Using a 1 mg/ml chloroform solution of PDtBF
The FA curve was determined and the results are shown in Figure 1b.
Next, LB was laminated with 1 and 20 layers at a surface pressure of 20 dyne/cm.
A membrane was created. The total film thickness is 220A, and the film thickness per layer is equivalent to 11A. As a result of performing differential interference microscope observation in the same manner as in Example 1, at least
No film defects larger than 0.05 μm were observed. Dry this LB membrane at 100 °C under an argon atmosphere for 12
After a period of time, microscopic observation and film thickness measurement were performed again, but no changes were observed. Example 2 20 layers of PDtBF were accumulated as in Reference Example 6.
Conductivity measurements were carried out by providing a counter electrode on the LB film in the same manner as in Reference Example 5, and the results showed good insulation properties of 10 ^-13 S/cm or less at 20°C, which reached 160°C in temperature raising experiments. No change in insulation properties was observed.
Also, ITO/PDtBF−LB when one layer is accumulated
The three-layer structure of film/Al corresponded to a thyristor and exhibited IV characteristics characteristic of a thyristor. Reference example 7 Same as reference example 4, but instead of PDiPF
Using a 1 mg/ml chloroform solution of PDcHF
The FA curve was determined and the results are shown in Figure 1c.
Next, we created a 20-layer LB film with a surface pressure of 20 dyne/cm. The total film thickness is 220A, and the film thickness per layer is equivalent to 11A. As a result of performing differential interference microscope observation in the same manner as in Example 1, it was found that at least 0.05 μm
No film defects above were observed. Dry this LB membrane at 100 °C under an argon atmosphere for 12
After a period of time, microscopic observation and film thickness measurement were performed again, but no changes were observed. Example 3 The LB film of Reference Example 7 was provided with a counter electrode in the same manner as in Example 1, and the conductivity was measured.
It exhibited good insulation properties of less than 10 ^-13 S/cm, and no change was observed in the insulation properties even at temperatures up to 160°C in temperature-raising experiments. In addition, this ITO/
The three-layer structure of PDcHF-LB film/Al corresponds to a thyristor and exhibited -V characteristics unique to thyristors. Example 4-12 A polyfumarate LB film was prepared in the same manner as in Reference Example 4, but under the conditions shown in Table 1. As a result of differential interference microscopy observation in the same manner as in Reference Example 4, no film defects of at least 0.05 μm or more were observed. Dry this LB membrane at 100 °C under an argon atmosphere for 12
After a period of time, microscopic observation and film thickness measurement were performed again, but no changes were observed. In addition, as in Example 1, a counter electrode was provided and current-voltage measurements were performed, and the results showed the characteristics shown in Table 1. In the temperature increase experiment, no change was observed in these characteristics even when the temperature reached 160°C. Ta. Example 13 An LB film in which one layer of PDiPF was laminated was prepared in the same manner as in Reference Example 4 except that GaP was used for the substrate. As a counter electrode, AL was deposited to a thickness of about 200 A in the same manner as in Example 1, and the current-voltage characteristics were measured. As a result, a good rectifying effect was observed, and the i-Si/
It was confirmed that the three-layer structure of PDiPF-LB film/Al works as an MIS type device. Furthermore, when this element is irradiated with white light of 0.4 mW/cm ² , Figure 3b
It was found that it has photoelectric conversion ability. Example 14 Example 13 except that (GaP) _0.9 −AS _0.1 was used for the substrate
LB was formed in the same manner as in Example 13, and after one layer of PDiPF was laminated, a counter electrode was provided in the same manner as in Example 13. When a DC potential of 5V is applied to this element, it emits red light,
It was found that it can be applied to light emitting diodes, electroluminescent displays, etc. Examples 15-20 The polyfumarate shown below was synthesized according to the method of Reference Example 1, and the polymer was synthesized according to the method of Reference Example 4.
An LB film was prepared, and a counter electrode was provided according to the method of Example 1, and the current/voltage characteristics were measured. Table 1 shows the configuration and electrical characteristics of these electrical elements. Example 15 Poly(2-cyanoethyl-isopropyl fumarate) Example 16 Poly(glycidyl-isopropyl fumarate) Example 17 Poly(diethylphosphonomethyl-isopropyl fumarate) Example 18 Poly(2-methylthioethyl-isopropyl fumarate) Example 19 Poly(2-perfluorooctylethyl-usopyropyl fumarate) Example 20 Poly(3-tristrimethylsiloxysilylpropyl-isopropyl fumarate)

【table】 [Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between surface pressure and surface area of a polymer LB film. a…Surface pressure-surface area curve at 20°C of PDiPF described in Reference Example 4, b…Surface area curve described in Reference Example 5
Surface pressure-surface area curve of PDtBF at 20℃, c
...Surface pressure-surface area curve at 20°C of PDeHF described in Reference Example 6. FIG. 2 is a current-voltage characteristic diagram at 20° C. of the thyristor described in Example 1. Figure 3 is an example
15 is a current-voltage characteristic diagram of the MIS type element described in No. 14. FIG. a...Current-voltage characteristics in the dark, b...Current-voltage characteristics in the light (white light 0.4 mW/ ^cm2 ).

Claims (1)

[Claims] 1. A polyfumarate represented by general formula (1) is made into a solution with a concentration of 0.1-3 mg/ml in an organic solvent that is immiscible with water, and the solution is gently spread on a clean horizontal surface to remove the organic solvent. is evaporated to form a gas film with a surface pressure of 1 dyne/cm or less, and a monomolecular solid film obtained by applying pressure in the horizontal direction to control the surface pressure to 10-30 dyne/cm is produced using the vertical dipping method or horizontal deposition method. A polymer LB film electrical element in which a conductive or semiconductor electrode is placed on a polymer LB film accumulated on a conductive or semiconductor substrate. embedded image In formula (1), R is a group selected from any of the following (a) to (b). (a) A branched hydrocarbon group with a carbon number of 3 to 30, with the first branching point inside the third carbon when counted from the fumarate ester, and the next branching occurs from one branching point in the same way. A hydrocarbon group having 3 or less carbon atoms up to the point. (b) Does not contain mobile hydrogen such as primary amide, secondary amide, hydroxy, thiol, etc., and does not contain N, O,
It is a branched hydrocarbon group containing a heteroatom selected from P and S, and the number of constituent atoms excluding hydrogen is 3 to 30, and the first one within 3 constituent atoms when counted from the fumarate ester. A hydrocarbon group that has a branching point and the number of constituent atoms from one branching point to the next branching point is 3 or less. (c) A fluorine-based hydrocarbon group selected from trifluoromethyl, pentafluoroethyl, hairtafluoro-n-propyl, or a group in which part or all of the hydrogen atoms in the hydrocarbon group in (a) are replaced with fluorine. . (d) A siloxane hydrocarbon group that does not contain a hydroxy group and has the same number of constituent atoms and branching as in (b).