Question

What is the SN2 reaction? How does Br attach to which carbon as a nucleophile and why? Difference between Unimolecular or Bimolecular? How NaBr and H₂SO₄ work in the reaction? Why Water/Sulfuric Acid/Brine/Sodium Hydroxide/Na₂SO₄ in Extraction? What does each layer have inside in each step of the separation?

Please help. Due to corona, this is a theoretical lab and I am very confused.

Chapter 16. The Sy2 Reaction: 1-Bromobutane Handout by Dr. Zhiyong Wang CH3CH2CH2CH, OH NaBr, H2SO4 ©Dr. Wang CH3CH2CH2CH„Br + NaHSO4 + H2O side reactions: CH,CH,CH,CH,OH H2804. CH3CH2CH=CH2 + CH3CH2CH2CH OCH CH2CH2CH3 1-butanol 1-butene di-n-butyl ether All these three materials are soluble in concentrated H2SO4. Purpose: To perform our first organic reaction and to practice the techniques of distillation and extraction. Modified Procedure: First prepare a sand bath of -110 °C. (The suggested hot place temperature setting is -200 °C. You need to check and modify it periodically to get a bath temperature of 110 °C.) You Place a 5-mL round-bottomed, short-necked flask in a small beaker on a balance and zero the reading. Use pipette to carefully add -0.80 g of 1-butanol. Record the exact balance reading on your notebook. Weigh -1.33 g of sodium bromide on a weighing paper and pour the solid into the flask. Try to get close to the specified weight, but if you measure a little bit more or less chemical than what is needed go with it. If there is any uncertainty as to whether you need to redo the operation please check with the instructor. Take the flask back to your hood, and then add one piece of boiling stone and 1.5 mL of water to the flask. Obtain 1.1 mL of concentrated sulfuric acid in a 10-ml graduated cylinder, hold the flask with a test tube holder inside the hood, and use a pipette to cautiously add the sulfuric acid, while constantly swirling, dropwise to the mixture in the flask. (Caution: concentrated sulfuric acid is strongly corrosive. If your hand gets in contact with any liquid immediately stop your operation, wipe it away with dry paper towel, and rinse your hand with running water for at least 15 minutes. It is recommended that you wear gloves for this experiment.) Refer to Fig. 1 on page 3 of this handout, fit the flask with a distillation head, a thermometer, and a 10-ml Erlenmeyer flask as the receiving vial. Immerse the whole apparatus close to the bottom of the sand bath, and reflux (boil) the reaction mixture for 45 minutes, taking care to prevent significant distillation of liquid into the receiving flask. Counting of time should start when the mixture begins to boil vigorously. After 45 minutes of heating further increase the bath temperature to -180 °C and distill for 15 minutes. Record the temperature of the distillate (product). The product collected in the Erlenmeyer flask is an azeotrope of 1-bromobutane and water containing some sulfuric acid, 1-butene, unreacted 1-butanol, and di-n-butyl ether because a couple of side reactions will take place. The residue in the round-bottomed short-necked flask contains strongly acidic inorganic by-

Answer 1

What is the SN2 reaction?

SN2 reaction is bimolecular nucleophilic substitution reaction. Here the two molecule involved in the rate determining step. Here the attacking and leaving at same time with the formation of transition state. In SN2 reaction always the backside attack of nucleophile, the inversion of stereochemistry takes place (Walden inversion).

  

Example: SN? Reaction (Bimolecular Reaction) Transition state Leaving group Nu Backside attack CH3 - ...ICH3 H3 C CH3 LG---------Nu - Нас · HzCim. Нас Nu + LG CH3 CH3 Substrate Electrophilic centre Partial bonds

SN1 reaction is Unimolecular nucleophilic substitution reaction. Here after the leaving carbocation intermediate forms. The nucleophile can attack on both the side. In SN1 reaction always racemization takes place.

Attack on both sides Example: Sn - Unimolecular Reaction Leaving group Intermediate H3C . ..CH CH₃ Substrate Carbocation CH3 CH3 LGCH3 "Nu — Nu Racemization ...ICH3 H3C "CH3 Electrophilic centre

Difference between Unimolecular or Bimolecular?

Unimolecular Reaction 1) Sn reaction 2) Unimolecular nucleophilic substitution reaction 3) Carbocation intermediate 4) After leaving then Attacking 5) Racemization takes place Bimolecular Reaction 1) SN? reaction 2) Bimolecular nucleophilic substitution reaction 3) Transition state 4) Attacking and leaving at same time 5) Inversion of stereochemistry

How does Br attach to which carbon as a nucleophile and why?

The Br attack on alpha carbon of hydroxy which becomes electrophilic centre after protonation of hydroxy as mechanism shown below. SN

reaction

Mechanism: SN - Reaction + - Na' Br - -HSO4 H3C B r + NaHSO4 + H20 H2S04 H3C non — H3cOH2 butan-1-ol Protonation Substrate Electrophilic centre 1-bromobutane Leaving group

Side reaction mechanism: H₃Cm oh H2SO4 -CH+ H₃C OH A SN1 Reaction H3C H₂C ~ OH Protonation butan-1-ol LI 1 Substrate Leaving group love pansion Lumina lunga SN2 Reaction CH, Нc Hс CH3 1-Butene di-n-butylether

How NaBr and H2SO4 work in the reaction?

Here Br is