Category: Chemistry Notes PPT

Before understanding the acidic nature of alkynes, it is vital to have an idea of what alkynes are in the first place. To be very specific, alkynes are unsaturated hydrocarbons. It means that they contain pi and sigma bond connections between hydrogen and carbon. Their general formula is C_nH_2n-2. They are highly reactive compounds and probably the most reactive of all compounds, especially when compared to alkanes as well as alkenes. They are the simplest hydrocarbons available right now.

A molecule of an alkyne contains a minimum of one triple linkage between a couple of carbon atoms. Take ethyne as an example here. CH=CH or ethyne strongly reacts with bases like sodamide and sodium metal (NaNH₂) to make sodium acetylide while liberating di-hydrogen gas. The whole procedure where alkynes respond to bases and release di-hydrogen gas proves the acidity of alkynes. 

HC ≡ CH + Na → HC ≡ C– Na⁺ + 1/2H₂

Understanding the Comparative Acidity of Alkynes

Alkynes are acidic because of their potential of dropping hydrogen atoms for creating alkynide ions. Hence, alkynes serve in the form of Bronsted-Lowry acids. As has already been pointed out earlier, alkynes contain a triple bonded atom of carbon which is called “sp” hybridised. 

Because of the maximum percentage or around 50% of the “s” character present in alkynes, “sp” hybridised orbitals of the atom of carbon in alkynes display high electronegativity. The orbitals attract C-H linkages of alkynes to a considerable extent. It is one of the most important reasons why the molecules of alkyne can lose hydrogen atoms very easily, thus making way for alkynide ions. Therefore, you can rightly say that the atom of hydrogen attached to the triple bonded atom of carbon is acidic. It proves the presence of acidic hydrogen in alkynes.

Coming to the question of why alkynes are acidic in nature all over again, it is to be noted that the acidity of alkynes happens to be greater in comparison to the acidity of alkenes and alkanes. This is because the atoms of carbon in alkenes and alkanes are “sp²” and “sp³” respectively. Therefore, the molecules have a lesser percentage of the “s” character when compared to alkynes. 

Hence, in such cases, the electronegativity of the atom of carbon is lesser when compared to alkynes. It is only because of this reason that alkenes and alkanes do not react with bases for liberating hydrogen gas. Further, it should be noted that only the atom of hydrogen attached to the triple linked atom of carbon is acidic and not the other atoms of hydrogen present within the alkyne series. The general trend of acidity in alkynes is presented like this:

HC≡CH > HC=CH₂> CH₃–CH₃

HC≡CH>CH₃–C≡CH>>CH₃–C≡C–CH₃

Understanding the Acidic Character of Alkynes

                                            (-)(+)

2HC = CH + 2Na -> 2HC = CNa + H₂

Acetylene                   Sodium acetylide   

                                   

This equation depicts the acidic character of alkynes. 

The acidic character of alkynes is also dependent on the unchanging nature of the formed conjugate base to a considerable extent. When the terminal alkynes happen to lose protons, the process gives way to the formation of acetylide ions that act in the form of a steady conjugate base. As has already been pointed out, sp-hybridised carbon has an electronegative nature. This is mainly because it contains 50% of the s-character and thus can hold a negative charge most effectively. Therefore, terminal alkynes are acidic.

What Atom Causes Acidity?

Coming to the question of what atom causes acidity in alkynes, it can rightly be said that the acidic nature of an alkyne is because of the presence of a high percentage of the s-character in the sp-hybridised orbitals. The s-character connects with the hydrogen atom s-orbital for forming a covalent bond. 

It is the high percentage of the s-character in the sp-hybridised atom of carbon that causes the O bond’s overlap area to move very close to the atom of carbon. The whole procedure leads to bond polarisation which further causes the atom of hydrogen to become positive but very slightly. However, it is this minuscule positive charge that makes the atom of hydrogen a very weak proton that can easily be removed with the use of a solid base.

On the other hand, s-character in hybridised carbon bonds tends to be less in alkenes and alkanes. This makes way for lesser electronegative carbon atoms corresponding to less movement towards the atoms present in the overlap area of the O bond. It is the location of the overlap area that makes all the corresponding atoms of hydrogen less deficient in electrons and hence less acidic as well. The reality is that the atoms of hydrogen linked to alkenes and alkanes can easily be removed in the form of protons, provided there is the availability of strong as well as non-aqueous bases.

Relative Acidity of Alkynes

Alkyne’s acidity stems from its tendency to lose hydrogen atoms and create alkylidenes. As a result, alkynes function as Bronsted-Lowry acids. In alkynes, the triple bound carbon atom is “sp” hybridised. The “sp” hybridised orbitals of carbon atoms in alkynes have a high electronegativity due to the large percentage of “s” character (50%) in alkynes. The C-H bond of alkynes is strongly attracted by these. Alkyne molecules may easily lose hydrogen atoms and create alkynide ions as a result. As a result, the hydrogen atom connected to the triply bound carbon atom has an acidic character.

Because the carbon atoms in alkanes and alkenes are “sp³” and “sp²” hybridised, the acidity of alkynes is larger than that of alkanes and alkenes. As a result, compared to alkynes, these molecules have a lower fraction of “s” character. As a result, the carbon atom’s electronegativity is lower in these situations than in alkynes. As a result, alkanes and alkenes do not display hydrogen gas liberation reactions with bases. It’s also worth noting that only hydrogen atoms linked to a triply bonded carbon atom are acidic, not the hydrogen atoms in the rest of the alkyne chain. The following is the overall trend in acidity:

HC≡CH > H₂C=CH₂> CH₃–CH₃

HC≡CH>CH₃–C≡CH>>CH₃–C≡C–CH₃

Hybridisation Effect

The stability of the related carbanions generated by deprotonation might explain the significant rise in acidity of terminal alkynes compared to other hydrocarbons. The suffix “-ide” denotes that the molecule is a negatively charged ion in the nomenclature of organic compounds.

The type of the hybridised orbital occupied by the lone pair of electrons determines
the carbanion’s stability. The lone pair in ethane occupies an sp³ orbital, while it occupies an sp² orbital in ethene and an sp orbital in acetylene, as indicated above. The “s” character in the sp³, sp², and sp orbitals is 25 percent, 33 percent, and 50 percent, respectively. A hybrid orbital with a greater “s” character will efficiently stabilise the negative charge since “s” orbitals are closer to the positively charged nucleus. In the presence of a suitable base, the acetylide ions will be the most stable and easily produced.

Conclusion

Alkynes contain pi and sigma bond connections between hydrogen and carbon. They are highly reactive compounds and probably the most reactive of all compounds. The whole procedure where alkynes respond to bases and release di-hydrogen gas proves the acidity of alkynes.

Introduction

Organic chemistry has always been a wider research subject among science enthusiasts. The basic organic chemistry’s idea is to propagate the elementary information about the organic compounds, exist around us and provide a solid foundation concerning the further exploration of organic compounds and factors that govern the properties of these compounds.

The organic compounds form a series, called homologs series, where the successive compounds contain similar functional groups and vary from one another by a –CH2 group. Alcohol is one of the various functional groups that are found in organic compounds. Let us discuss more on the structure of alcohol, phenol, and others.

What is Alcohol?

Alcohols are organic compounds, where an aliphatic carbon or a hydrogen atom is replaced with the hydroxyl group. Therefore, an alcohol molecule consists of two parts; one containing the alkyl group and another containing the hydroxyl group, and they have a sweet odor. They exhibit a unique set of both physical properties and chemical properties. The both physical and chemical properties of alcohol are primarily due to the hydroxyl group presence. The alcohol structure depends on different factors.

Alcohols are classified into various groups based on where the hydroxyl group is placed in the molecule. This results in a few differences in the chemical properties. The classification of alcohol is given as follows:

Primary Alcohols

In primary alcohol, the carbon with the hydroxyl group will only be attached to a single or one alkyl group.

Some examples of primary alcohols are given below in the diagrammatic representation.

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Methanol is an exception to the above representation. Still, it is the primary alcohol though the carbon, having the hydroxyl group attached does not have any other alkyl group attached to it.

Secondary Alcohols

In secondary alcohol, the carbon with the hydroxyl group will be attached to the two alkyl groups.

Some examples of secondary alcohols are represented below:

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Tertiary Alcohols

The carbon present with the hydroxyl group gets attached to three other alkyl groups in the tertiary alcohol.

Some examples of tertiary alcohols are depicted below.

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Alcohol Structure

The alcohol atomic structure is primarily attributed to the presence of the hydroxyl group alcohol. In alcohols, the main chain’s carbon atom gets bonded to the oxygen atom of the hydroxyl group alcohol by a sigma (σ) bond.

This sigma bond is formed because of the overlap of an sp3 hybridized orbital of carbon with an oxygen atom’s sp3 hybridized orbital. Because of the repulsion between the unshared electron oxygen pairs, the bond angle of the C-O-H bonds present in alcohol is slightly less than that of the tetrahedral angle (109°-28′).

The structure of Alcohol can be represented as follows:

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Structure of Phenol

Phenol structure is primarily attributed to two main factors, as listed below:

• The partial double bond character because of the resonance occurs in the aromatic ring due to a conjugated electron pair of oxygen.

• Hybridization is the carbon to which the oxygen atom of the hydroxyl group is. The carbon atom attached to the oxygen is sp2 hybridized in phenol.

Hence, the C-O bond length in phenol is slightly less than that of methanol.

The structure of phenol can be represented as below:

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Ether Structure

• An ether molecule contains a tetrahedral structure.

• Because of the repulsive interaction between the two bulky (–R) groups, the bond angle (R-O-R) is a bit greater than the tetrahedral angle.

• The C–O bond length present in ether is almost similar to that as in alcohol.

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Nomenclature of Alcohol

Etymology

The term “alcohol” is introduced from an Arabic word, Arabic kohl, which is a powder used as an eyeliner. Al- is the definite article of Arabic that is equivalent to the in English. Alcohol was originally used for the fine powder, which is formed by the natural mineral stibnite sublimation to produce the antimony trisulfide Sb2S3.

It was also considered to be either as “spirit” or “essence” of this mineral. Moreover, it was used as an eyeliner, cosmetic, and antiseptic. Generally, the meaning of alcohol was extended to the distilled substances and then narrowed to ethanol, when a synonym, “spirits” was for hard liquor.

In the translation of John of Vigo, in 1543, Bartholomew Traheron introduces the word “barbarous” as a term used by authors for “fine powder.” He wrote, “the barbarous authors use alcohol, or (sometimes I find it as written) alcohol, for the finest powder.”

Lexicon Chymicum, in 1657, by William Johnson, glosses the word as “antimonium sive stibium.” By extension, the same word had come to refer to any fluid come by distillation, including “alcohol of wine,” the distilled essence of wine. Also, in 1594, Libavius in Alchymia referred to as, “vini alcohol vel vinum alcalisatum.”

Ethanol was invented in 1892 by combining the word ethane with “-ol” and ending up with “alcohol”.

An alloy could be a mixture of metals or metals combined with one or more other elements. Elemental iron produces alloys called steel or silicon steel when it is combined with non-metallic carbon or silicon. The resulting mixture forms a substance with properties that always differ from those of the pure metals, like increased strength or hardness.

Alloys have a metallic bonding character. Alloys are usually classified as substitutional or interstitial alloys, relying on the atomic arrangement that forms the alloy. they will be further classified as homogeneous (consisting of 1 phase), or heterogeneous ( consisting of two or more phases) or intermetallic.

Transition Metal  

The transition metals are a gaggle of metals that are found within the middle of the periodic table. The alkaline earth metals, beginning with beryllium are to the left and thus the boron group elements are to the right.

Atomic numbers of these metals are from 21-30, 39-48, 57, 72-80, 89, and 104-112. Many elements like Zn, Cd, Hg, La, and Ac have a highly debatable position within the transition series of elements. La and Ac also are classed within the series and actinide series respectively.

Transition metals have several properties. they’re harder and fewer reactive than the alkaline-earth metal metals. they’re harder than the post-transition metals. they will make colorful chemical compounds with other elements. Most of them have quite one oxidation number. They’re electrical conductors a bit like other metals.

Properties of Alloys

Individual pure metals possess useful properties like good electrical conductivity, high strength, and hardness, or heat and corrosion resistance. Commercial metal alloys plan to combine these beneficial properties so on make metals more useful for particular applications than any of their component elements.

Steel requires the proper combination of carbon and iron (about 99% iron and 1% carbon) to supply a metal that’s stronger, lighter, and more workable than pure iron.

Precise properties of latest alloys are difficult to calculate as elements don’t combine to become a sum of the parts. They form through chemical interactions, depending upon component parts and specific production methods. As a result, much testing is required during the event of the latest metal alloys.

Melting temperature may be a key thing about alloying metals. Galinstan, a low-melt alloy containing gallium, tin, and indium, is liquid at temperatures above 2.2°F (-19°C), meaning its melting point is 122°F (50°C) but pure gallium is quite 212°F (100°C) below indium and tin.

The Explanation for Alloy Formation 

The atomic sizes of transition metals are almost like each other and this attributes to their nature of forming alloys. Because the atomic sizes are very similar, one metal can replace the other metal from its lattice and form a primary solid solution. This primary solid solution is understood as an alloy. This is often rational why transition metals are miscible with one another in a molten state. When the molten solution cools down, the corresponding alloy formation takes place.

Different Types of Alloy

There are different types of alloys that are prepared consistent with the specified properties and therefore the area of application. The important types and their uses are:

Bearing Alloy – These are made to accommodate the high when there’s a sliding contact with another body mentioned as a shaft of motor, generators or vehicles.

Corrosion-Resistant – Noble metals are utilized in this case. These noble metals initially oxidize and act as a separation layer which prevents chemical change from the opposite metals. The alloys of aluminum function as the only corrosion resistors.

Fun Facts

• The alloy, sterling silver, is an alloy that consists mainly of silver. Many alloys that have the word “silver” in their names are only silver in color. nickel silver and Tibetan silver are samples of alloys that have the name but don’t contain any elemental silver.

• It is believed that steel is an alloy of iron and nickel, but it consists mainly of iron, carbon, and any of several other metals.

• Electrum could also be a gift alloy of gold and silver with small amounts of copper and other metals. Considered by the traditional Greeks to be “white gold,” it had been used as far back as 3000 B.C. for coins, drinking vessels, and ornaments.

• Gold can exist in nature as a pure metal, but most of the gold we get to see is an alloy. The quantity of gold within the alloy is expressed in terms of karats, so pure gold is pure gold, 14-karat gold is 14/24 parts gold, and 10-karat gold is 10/24 parts gold or but half gold. 

• Amalgam is an alloy that is made by combining mercury with another metal. most metals form amalgams, with the exception of iron. Amalgam is put to use in dentistry and in gold and silver mining because these metals readily combine with mercury.

Ammonia is a pungent and colorless substance, which is composed of nitrogen and hydrogen. It is one of the simplest stable compounds of these elements, and it serves as a starting material for the formation of several commercially essential nitrogen compounds.

The chemical formula of ammonia is given as NH3.

Structure

The ammonia molecule contains a trigonal pyramidal shape, which is predicted by the VSEPR theory – Valence Shell Electron Pair Repulsion with an experimentally described bond angle of 106.7°. The central nitrogen atom contains 5 outer electrons, including an additional electron from every hydrogen atom. This gives a complete set of four electron pairs of eight electrons that are arranged tetrahedrally. Three of these electron pairs are used as bond pairs, which leave a single lone pair of electrons.

The lone pair repel more strongly compared to the bond pairs; thus, the bond angle is not as expected, 109.5°, for a regular tetrahedral arrangement, but it is 106.7°. This specific shape gives the molecule a dipole moment and makes it polar.

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Industrial Production of Ammonia

Industrially, the global production of ammonia in 2018 was listed as 175 million tonnes, with zero significant change relative to 2013’s global industrial production, which is given as 175 million tonnes. Industrial ammonia is sold either in the form of ammonia liquor (generally 28% of ammonia in water) or as refrigerated or pressurized anhydrous liquid ammonia, which is transported in cylinders or tank cars.

NH3 boils at a temperature of −33.34 °C  and at a pressure of one atmosphere, and because of that, the liquid should be stored at low temperature or under pressure. hydroxide or Household ammonia is a solution of NH3 in water. Such concentrated solutions are measured in the Baumé scale units (density), with 26 degrees of Baumé (by weight – about 30% ammonia at 59.9 °F or 15.5 °C) being a typical high-concentration commercial product.

Etymology

Pliny, in a book, refers to a salt produced in the Roman province of Cyrenaica named hammoniacum, so-called due to its proximity to the nearby Temple of Jupiter Amun. However, the description given by Pliny on salt does not conform to the ammonium chloride properties. According to the commentary of Herbert Hoover in his English translation of Georgius Agricola’s De re Metallica, it is more likely to have been common sea salt. Ultimately, in any case, that salt gave ammonium and ammonia compounds their name.

Natural Occurrence

Ammonia can be found chemically in trace quantities in nature, being formed from nitrogenous vegetable and animal matter. Both ammonium and ammonia salts are also found in the fewer quantities in rainwater, whereas ammonium sulfate and ammonium chloride (sal ammoniac) are found in volcanic districts; ammonium bicarbonate crystals have been found in the Patagonia guano. The kidneys secrete ammonia in excess acid neutralization. Ammonium salts can also be found distributed in seawater and through fertile soil.

Amphotericity

The most characteristic properties of ammonia are given as its basicity and is considered to be a weak base. It also combines with acids to produce salts; hence with hydrochloric acid, it forms ammonium chloride, ammonium nitrate, nitric acid, etc. Perfectly dry ammonia will not always combine with perfectly dry hydrogen chloride. Moisture is required to bring about the reaction. Opened bottles of the concentrated hydrochloric and ammonia acid produce clouds of ammonium chloride as a demonstration experiment, which seems to appear “out of nothing” because the salt produces where the two diffusing clouds of molecules meet, at some point between the two bottles.

NH3 + HCl → NH4Cl

The salts, which are produced by the ammonia action on acids, are called ammonium salts, and all contain ammonium ion (NH4+).

Formation of Other Compounds

In organic chemistry, ammonia acts as a nucleophile in substitution reactions. Amines are formed by the ammonia with alkyl halide reaction, although the resulting -NH₂ group is nucleophilic, and the secondary, tertiary amines are often resulting as byproducts. An ammonia excess helps to minimize the multiple substitutions and neutralizes the formed hydrogen halide. 

Methylamine can be commercially prepared by the ammonia with chloromethane reaction, and the ammonia with 2-bromopropanoic acid reaction has been used to prepare the racemic alanine in the yield of 70%. Ethanolamine can be prepared by a ring-opening reaction with ethylene oxide, which sometimes, the reaction is allowed to proceed further to form “di” and triethanolamine.

Ammonia as a Ligand

Ammonia acts as a ligand in the transition metal complexes. In the middle of the spectrochemical series, it is a pure σ-donor and exhibits intermediate hard-soft behavior. The relative donor strength of this acid toward a series of acids versus other Lewis bases can be illustrated by the C-B plots. For historical reasons, ammonia is named as ammine in the coordination compound’s nomenclature.

A few notable ammine complexes are given as tetraamminediaquacopper (II), with the chemical formula [Cu(NH3)4(H2O)2]2+), which is a dark blue complex formed by adding ammonia to a copper(II) salt solution.

What do Antibiotics do?

Antibiotics are a group of powerful medicines which fight against infections and can also save our lives when we use them correctly. They work either by stopping the bacterial reproduction or by destroying them completely. However, before bacteria are multiplied and cause symptoms, our immune system kills them. The white blood cells attack the harmful bacteria and even though it causes symptoms, our immune system can usually cope and fight with the infection. However, sometimes, when the harmful bacteria are excessive in number and our immune system cannot fight them, antibiotics are used.

If you know what is penicillin, you would know that it was the first-ever antibiotic to be discovered. There are several penicillin-based antibiotics like amoxicillin, ampicillin, and penicillin G, which are used even today in the treatment of several infections. There are many topical antibiotics available as well in the form of OTC ointments and creams.

Today we will discuss what are antibiotics, what do antibiotics do, what are antibiotics used for, and how long do antibiotics take to work.

Antibiotics Definition

Let us now discuss the antibiotic meaning and its definition.

Antibiotics are defined as a type of an antimicrobial drug that is used for treating and preventing bacterial infections through the inhibition of the growth of bacteria. Antibiotics are not effective on the diseases that are caused due to viruses, like flu or cold.

History of Antibiotics

Let us discuss the penicillin meaning, penicillin history, how penicillin work, and take a look at what penicillin is used for.

Initially, the antibiotics were obtained from microorganisms. In the later years after the advancement of synthetic methods, antibiotics were developed synthetically.

In the nineteenth century, a German bacteriologist, Paul Ehrlich, started to look for a chemical which could kill bacteria in both the bodies of humans as well as animals, but which does not affect their health. After conducting several types of research, he discovered a medicine called arsphenamine, which is also called salvarsan. It was used in the treatment of syphilis, caused by the bacteria spirochete. He received a Nobel Prize for the same in the year 1908. Though this medicine had some side effects, its impact on the bacteria was so much more than on the humans.

In the year 1932, another drug known as prontosil was discovered by the group of researchers located at Bayer Laboratories. This was much similar to salvarsan that tends to convert into sulphanilamide when taken into the body.

However, the actual transformation in regards to the antibacterial therapy happened with the discovery which was made by Alexander Fleming in the year 1929, of the naturally developed antibiotic called penicillin.

How do Antibiotics Work?

Although there are many different kinds of antibiotics, they tend to work in two basic ways.

1. Certain antibiotics like penicillin tend to get rid of the bacteria when they kill it. They usually do so by disrupting the formation of the cell content or the cell wall of the bacteria.

2. The other kind of antibiotics tends to inhibit the multiplication action of the bacteria.

Types of Antibiotics

Antibiotics are typically classified depending on their chemical structure. Antibiotics having the same structural class have similar properties when it comes to effectiveness, allergy potential, and toxicity. They are:

1. Penicillins

2. Macrolides

3. Sulfonamides

4. Cephalosporin

5. Tetracyclines

6. Fluoroquinolones

7. Aminoglycosides

Depending on how they work to stop the bacterial infection, they are classified as follows:

• Bactericidal: They tend to kill the bacteria that is present in the body that causes diseases. Examples include penicillin, polymyxin, etc.

• Bacteriostatic: They are the medicines that are used for inhibiting microbial growth. The examples include Chloramphenicol, Tetracycline, etc.

Depending on the range of action of antibiotics, they are classified as follows:

These are the drugs which inhibit or destroy the growth of a huge range of both the gram-positive and the gram-negative bacteria. For e.g;  Amoxicillin

These types of antibiotics typically attack Gram-positive bacteria or gram-negative bacteria. For e.g; Penicillin G

These antibiotics are effective against a particular type of organism or even a disease.

What is Antibiotic Resistance?

The emergence of bacterial resistance to antibiotics is quite a common phenomenon. The emergence of bacterial resistance tends to often reflect on the evolutionary processes which take place during the time of the antibiotics therapy. The treatment of antibiotics might tend to select for the bacterial strains having genetically or physiologically enhanced capacity for surviving higher doses of the antibiotic medication. Under a few conditions, it can result in a preferential resistant bacterial growth, whereas the susceptible bacterial growth gets inhibited by the antibiotic.