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CHEMICAL TERRORISM The deliberate release of certain chemicals could poison people. Chem Factsheet September 2002 Number 39 Reactions of Benzene and its Compounds To succeed in this topic you. No part of these Factsheets may be reproduced.
Chemical Bonding Basics In bonding, atoms lose, gain, or share electrons in order to have the same number of electrons as the noble gas that’s nearest on the periodic table. Ionic, covalent, and metallic bonds are formed by combinations of metals and nonmetals. Metal + nonmetal = ionic bond. Nonmetal + nonmetal = covalent bond.
Metal + metal = metallic bond When two elements engage in ionic bonding, one or more electrons are transferred from the metal to the nonmetal, forming ions (charged atoms). The metal, having lost one or more electrons, forms a cation, an ion with a positive charge; the nonmetal, having gained one or more electrons, becomes an anion, an ion with a negative charge. When two elements form a covalent bond, one or more electron pairs are shared between these two elements. In metallic bonding, which occurs in metals (either a pure metal or an alloy of two or more metals), the valence (outer shell) electrons are donated to a “sea of electrons.”. Chemistry Concepts: Energy Levels and Orbitals A lot of chemistry is explained by the sharing and trading of electrons between atoms. Understanding how electrons are arranged in an atom is a building block of Chem I. Electrons in an atom are contained in specific energy levels (1, 2, 3, and so on) that are different distances from the nucleus.
The larger the number of the energy level, the farther it is from the nucleus. Electrons that are in the highest energy level are called valence electrons. Within each energy level is a volume of space where specific electrons are likely to be located. These spaces, called orbitals, are of different shapes, denoted by a letter (s, p, d, f, g).
(In most cases, only the electrons contained in the s and p orbitals are considered valence electrons.) Electrons seek the lowest energy level possible. The following electron-filling pattern indicates how the electrons fill into the energy levels. Knowing this pattern is useful in many aspects of chemistry, including predicting the bonding situation of a particular atom and in the prediction of the geometry of a covalent compound. Electron filling pattern: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f.
Digging the Mole Concept in Chemistry The mole (abbreviate mol and sometimes called Avogadro ‘ s number) is a conversion number that allows a chemist or chemistry student to move from the microscopic world of atoms, ions, and molecules to the macroscopic world of grams, kilograms, and tons. The mole is used in reaction stoichiometry to predict how much product can be made from a certain amount of reactant or how much reactant is required to produce a certain amount of product. If you know the particles, moles, or grams of a substance, you can calculate the other two measurements by using the following equation: 1 mole = 6.022 × 10 23 particles/mol = formula weight expressed in grams. Common Measurement Conversions for Chemistry In order to succeed in your Chem I class, you need to have a firm understanding of basic chemistry measurements and how to convert them from one measurement to another. Following are some important conversions of temperature, size, and pressure as well as metric prefixes to memorize for your chemistry class: Temperature conversions:. °F = 9/5(°C) + 32.
°C = 5/9(°F – 32). K = °C + 273 English/metric conversions:. 1 in = 2.54 cm.
1 lb = 454 g. 1 qt = 0.946 L Pressure conversion:. 1atm = 760 mmHg = 760 torr Common metric prefixes:. milli- = 0.001. centi- = 0.01. kilo- = 1,000. The Basic Chemistry of Acids and Bases A lot of chemistry requires you to understand the difference between acids and bases.
An acid is a substance that donates an H + ion to another chemical species called a base. A base is a substance that accepts (combines with) an H + ion. If you need to know the concentration of the H + ion in solution, you can do so by representing the H + molarity, H +. Another way to represent the H + concentration is the pH, which is the negative logarithm of the H + molarity. The following equation shows this mathematical relationship as well as the way to calculate the H + molarity given the pH: pH = –logH +; H + = 10 –pH. pH = 7 is neutral. pH less than 7 is acidic.
pH greater than 7 is basic. The Combined Gas Law and Ideal Gas Law When studying the properties of gases, you need to know the relationships between the variables of volume (V), pressure (P), Kelvin temperature (T), and the amount in moles (n) so that you can calculate missing information ( P, V, T, or n) and solve reaction stoichiometry problems. Although the pairs of variables have individual relationships, the two most important and useful gas laws are the combined gas law and the ideal gas law: Combined gas law ( P 1 V 1)/ T 1 = ( P 2 V 2)/ T 2 ( T must be in Kelvin) Ideal gas law PV = nR T (R = 0.0821 L atm/K.mol).
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Chem Factsheet September 2002 Number 39 Reactions of Benzene and its Compounds To succeed in this topic you need to:. Have a good understanding of AS-level Organic Chemistry (Factsheets 15, 16,17, and 27);. Be confident in using organic nomenclature and structural formulae. After working through this Factsheet you will:. Be able to explain the structure of benzene;.
Know the names and structures of common substituent products of benzene;. Know the necessary reactions of benzene and its compounds. Benzene, C6H6, is an aromatic hydrocarbon, or an arene.
When the formula was first found, the structure proposed initially was: H H H H This structure would have resulted in bonds having different lengths; double bonds are shorter than single bonds, due to the greater attractive forces. If this had been the correct structure, two equivalent forms would have existed: H H H H H H H H H H H H H H Derivatives of benzene Derivatives of benzene are formed by substitution reactions which will be electrophilic in nature due to the high concentration of electrons in the delocalised system of benzene. H H High concentration of electrons. Benzene attracts electrophiles. H H The group C6H5-, derived from benzene with one H atom having been substituted, is known as the phenyl group. Listed below are some common substituent products. Substituent group Methyl Chloro Nitro Hydroxyl Amino Carboxylic acid -CH3 -Cl -NO 2 -OH -NH 2 -COOH Systematic name Methylbenzene Chlorobenzene Nitrobenzene Phenol Phenylamine Benzenecarboxylic acid H H Reactions of benzene Candidates are expected to be able to recall the following reactions, in terms of reagents and reaction conditions.
Nitration of benzene. Benzene reacts with a mixture of concentrated nitric acid and concentrated sulphuric acid (called a nitrating mixture) at 50oC to form nitrobenzene. NO 2 + HNO 3 conc H2SO4 50o C However, where equivalent bond structures can be written for a compound neither exist. Instead, all bond lengths will be equal as the available electrons are shared equally amongst the atoms involved. The benzene ring consists of 6 C-C single bonds and the remaining electrons exist in a delocalised system. The structure of benzene is often written: + H2 O Reaction type: Substitution Conditions: Conc. H2SO4, 50oC Mechanism: Electrophilic Exam Hint: - This is a commonly examined reaction.
Candidates should pay careful attention to the mechanism of this reaction – see Factsheet 40. In this representation the H atoms need not be shown. Gta sa save file 100 programs. The C-C bonds are somewhere between single and double bonds, as illustrated by the following bond length data: C-C single bond length in cyclohexene C=C double bond length in cyclohexene But C-C bond length in benzene = 0.14 nm = 0.15 nm = 0.13 nm 2. Bromination of benzene. Bromine reacts with benzene in the presence of an iron wire catalyst in dry conditions at room temperature and pressure. Br + Br 2 Fe Dry + HBr Benzene is a clear colourless liquid at room temperature and pressure.
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It is relatively unreactive due to the strong bonding within its structure Benzene used to be used as a non-polar organic solvent, but this is no longer the case due to its carcenogenic (cancer causing) properties. Reaction type: Substitution Conditions: Fe catalyst, dry, room temp. Mechanism: Electrophilic See Factsheet 40 for the reaction mechanism. 1 Reactions of Benzene and its compounds 3. Alkylation of benzene (Freidel-Krafts Reactions). Benzene reacts with chloroalkanes in the presence of anhydrous aluminium chloride to give an alkyl benzene. C 2H 5 + C2 H 5Cl AlCl3 Dry Chem Factsheet 1.
Reaction of phenol with sodium hydroxide. The -OH group in phenol is more acidic (proton donating) than in straight chain alcohols. Phenol is not very soluble in water, but forms a colourless solution with aqueous sodium hydroxide. OH O− (s) + OH−(aq) (aq) + H2O(l) phenate ion + HCl Reaction type: Substitution Conditions: Anhydrous AlCl3, dry, possible heat under reflux. Mechanism: Electrophilic A similar reaction takes place with acid chlorides, benzene and aluminium chloride to give ketones. CH 3 O C O AlCl 3 + CH 3 C + HCl Dry Cl Reaction type: Substitution Conditions: Anhydrous AlCl3, dry, possible heat under reflux. Mechanism: Electrophilic Again, see Factsheet 40 for the reaction mechanism.
Conditions: Aqueous NaOH at room temp. Note how phenol has acted as an acid, donating a proton to neutralise the hydroxide ion. Reaction of phenol with bromine water. Substitution of the hydrogen atoms on the benzene ring is made easier by the presence of the -OH group. OH (aq) + 3Br2(aq) Br Reaction type: Substitution Conditions: Bromine water added - no catalyst required. Mechanism: Electrophilic This reaction is easily observed as the red/brown bromine water decolourises and a white precipitate is formed.
Br OH Br (s) + 3HBr(aq) 4. Oxidation of side chains on arenes. If an arene (i.e. Benzene) with a carbon-containing side chain (with the C atom bonded directly to the ring structure) is heated under reflux with alkaline potassium manganate (VII) solution, benzenecarboxylic acid is formed. CH3 KMnO4 OH− COOH + H2O COOH + CO2 + 2H2O COOH + CO2 + H2O 3.
Reaction of phenol with acid chlorides. Phenol reacts with acid chlorides to form esters, but alkaline conditions are necessary as phenol does not react as readily as straight chain alcohols. O CH 3 C O OH O + HCl + CH 3 C Cl Conditions: Aqueous NaOH CH2CH2OH KMnO4 OH− CH2COOH KMnO4 OH − The carbon-containing side chain (whatever it is) is oxidised to –COOH. Reaction type: Oxidation Conditions: KMNO4 in alkali, heat under reflux Nitrobenzene Nitrobenzene C6H5NO2 is another common benzene derivative.
NO 2 Reactions of phenol. Phenol, C6H5OH is a common derivative of benzene. OH The reduction of nitrobenzene to an amine using tin and concentrated hydrochloric acid. Tin and concentrated hydrochloric acid are used as reagents to form an intermediate tin complex, then large quantities of alkali are required to release the amine after the initial reaction. NO 2 NH 3 Sn conc HCl Phenol is an alcohol, but whereas straight chain alcohols have just the -OH functional group, phenol has the -OH group and the electron- rich benzene ring. Care must be taken when using phenol, a white crystalline solid, as it is both corrosive and an anaesthetic. + 2− SnCl6 NH 3 + NaOH NH 2 2 2 Reaction type: Reduction Conditions: Tin, conc.
HCl, then large quantities of NaOH. Note: This reaction will work for other aromatic nitro-compounds. Other reducing agents (e.g. LiAlH4) can work. 2 Reactions of Benzene and its compounds Chem Factsheet Answers. Phenylamine Phenylamine C6H5NH2 is produced from nitrobenzene, as described above.
Strong carbon-carbon bonds due to delocalised system of electrons througfhout the ring structure. They are attracted to the electron rich delocalised system. Amines, being basic, usually react with acids to form salts. The following reaction, however, is different. (i) The reaction between phenylamine and nitrous acid First the unstable nitrous acid (HNO2) is produced in situ by reacting sodium nitrite with hydrochloric acid. NaNO2 (aq) + HCl(conc.) 3. Benzene is carcenogenic.
(a) reagents: conditions: (b) reagents: conditions: (c) reagents: conditions: conc. H2SO4, 500C Br2 (l) Fe catalyst, dry CH3Cl anhydrous AlCl3, dry, heat under reflux! HNO2 (aq) + NaCl(aq) (ii) The diazotisation reaction Phenylamine then reacts with the nitrous acid and HCl to form benzenediazonium chloride. NH 2 + HNO2 + HCl low temp 5. Phenol is more acidic than ethanol, it donates protons more readily. O CH 3 C OH + CH3 C O Cl O + HCl N + NCl − + 2H2O Diazonium ions are important intermediates.
(iii) The coupling reaction of benzenediazonium ions with phenol. Azo-dyes are formed as diazonium salts react with phenol. N + NCl + − OH low temp N N OH + HCl yellow precipitate (diazo compound) There are many diazo compounds with different colours, and they can be used in textile dyes. Explain the stability of the benzene ring structure. State what sort of species will attack the benzene ring, and why.
State why care should be taken when handling benzene. Give reagents and conditions for the following conversions: (a) NO 2 (b) (c) Br CH 3 Acknowledgements: This Factsheet was researched and written by Kieron Heath Curriculum Press, Unit 305B, The Big Peg, 120 Vyse Street, Birmingham, B18 6NF ChemistryFactsheets may be copied free of charge by teaching staff or students, provided that their school is a registered subscriber. No part of these Factsheets may be reproduced, stored in a retrieval system, or transmitted, in any other form or by any other means, without the prior permission of the publisher. ISSN 1351-5136 5. State why phenol reacts more readily with sodium hydroxide than ethanol.
Show how phenol can be used to form an ester.