Chemistry Presentation Forensic Sciences

Chemistry PPT

1. Organic Reactions What are Organic Reactions ? Organic reactions  are chemical reactions involving organic compounds. Many of these reactions are associated with functional groups. The general theory of these reactions involves careful analysis of such properties as the electron affinity of key atoms, bond strengths and  steric hindrance .

2. Types of Organic Reactions There are four main types of organic reactions that can take place. They are as follows: Substitution reactions Elimination reactions Addition reactions Rearrangement reactions

3. SUBSTITUTION REACTIONS The Substitution Reaction is defined as a reaction in which the functional group of one chemical compound is substituted by another group or it is a reaction which involves the replacement of one atom or a molecule of a compound with another atom or molecule. Example : CH 3 Cl reacted with a hydroxy ion (OH - ) will produce CH 3 OH and chlorine. CH 3 Cl + OH - = CH 3 OH + Cl

4. CH 3 Cl + OH - = CH 3 OH + Cl

5. Elimination Reaction Elimination reaction , any of a class of  organic  chemical reactions in which a pair of  atoms  or groups of atoms are removed from a molecule, usually through the action of acids, bases, or metals and, in some cases, by heating to a high  temperature .

6. 1. Reaction : Dehydration of 2-butanol to form 2-butene. CH3​CH2​​CH(OH)CH3 H 2 SO 4 ​​​CH3​CH=CHCH3​+H2​O Product : 2-butene 2. Reaction : Dehydrohalogenation of 2-bromo-2-methylpropane to form 2-methylpropene. Reaction : (CH3)3CBr+KOC(CH3)3→(CH3)2C=CH2+KBr+ROH Product : 2-methylpropene

7. ADDITION REACTIONS An addition reaction is a type of chemical reaction where two or more reactants combine to form a single product. This type of reaction is particularly common in organic chemistry, especially involving compounds with double or triple bonds.

8. TYPES OF ADDITION REACTIONS Electrophilic Addition : Involves the addition of an electrophile and a nucleophile to a molecule with a π bond (usually a double bond). The π bond breaks, and new σ bonds are formed. Examples : Hydrogenation : Addition of hydrogen (H₂) to an alkene to form an alkane . R-CH=CH-R’+H 2 → R-CH 2 ​-CH 2 ​-R’ Halogenation : Addition of halogens (e.g., Br₂) to an alkene to form a dihaloalkane . R-CH=CH-R’+Br 2 ​→R-CH(Br)-CH(Br)-R’

9. Nucleophilic Addition : Involves the addition of a nucleophile to an electrophilic site in a molecule, often seen with carbonyl compounds (like aldehydes and ketones ). Examples : Addition of Grignard Reagents: Reaction of a Grignard reagent (e.g., RMgX ) with a carbonyl compound to form an alcohol. R-CO- R’+RMgX → R-C(OH)(R’)- R’+MgX (or MgX 2 ​) Addition of Cyanide Ions : Reaction of a carbonyl compound with cyanide ions (CN⁻) to form a cyanohydrin . R-CO-R’+CN - →R-C(OH)(CN)-R’

10. REARRANGEMENT REACTIONS Rearrangement reactions are a type of chemical reaction where the structure of a molecule is reorganized to form a different structural isomer. In these reactions, the molecule undergoes a reorganization of its bonds and atoms, resulting in a product with a different connectivity or arrangement of atoms compared to the starting material.

11. EXAMPLES OF REARRANGEMENT REACTIONS Hydride Shift and A lkyl Shift ( Carbocation Rearrangement) : Example : 1,2-Hydride Shift in the Hydration of 3-Hydroxy-2-butanone. Reaction : In the hydration of 3-hydroxy-2-butanone, the formation of a more stable carbocation occurs through a hydride shift. CH 3 ​CH(OH)CH 2 ​ CH 2 ​CH 3 ​ → CH 3 ​CH 2 ​C(OH)HCH 2 ​CH 3 Wagner- Meerwein Rearrangement: Example : Rearrangement of 2,3-Dimethylpentane Reaction: In this reaction, a 2,3-dimethylpentane can undergo a rearrangement to form a more stable product by shifting a methyl group. (CH 3 ​) 2 ​CHCH 2 ​CH 2 ​CH 3 ​→CH 3 ​C(CH 3 ​)2​CH 2 ​CH 3 ​

12. SHAPES OF s, p, d ORBITALS s Orbitals : Shape : Spherical Characteristics : l = 0 : The quantum number ‘l’ for s orbitals is zero. Node : There are no angular nodes, only radial nodes. Density Distribution : Electron density is uniformly distributed around the nucleus in a spherical shape. Drawing : Imagine a sphere centered on the nucleus. The probability of finding an electron is highest near the nucleus and decreases with distance from the nucleus.

13. p Orbitals Shape: Dumbbell-shaped (or two-lobed) Characteristics: l = 1: The quantum number lll for p orbitals is one. Nodes : There is one angular node (a plane where the probability density is zero). Orientation : There are three p orbitals in each shell with l=1, oriented along the x, y, and z axes (denoted as p x , p y ​, and p z ​). Drawing : Each p orbital looks like a pair of lobes extending in opposite directions from the nucleus, separated by a nodal plane.

14. d Orbitals Shape : More complex, with cloverleaf or double-dumbbell shapes. Characteristics : l = 2 : The quantum number lll for d orbitals is two. Nodes : Each d orbital has two angular nodes. Orientation : There are five d orbitals in each shell with l=2. Drawing : Each d orbital has a more complex shape compared to s and p orbitals .