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Simun Mishra posted an Question

August 18, 2020 • 16:25 pm

30 points

IIT JAM
Chemistry (CY)

In case of grignard reagent x is always br and i or any other halogens ?

2 Answer(s)

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Dinesh khalmaniya 1

hope this will help you
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Dinesh khalmaniya 1 Best Answer

check it
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F is almost unreative so don't use in the preparation of RMgX
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why F is un reactive sir
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wait
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ok sir
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here RX react with Mg to form RMgX. so we will check the leaving group ability of X in RX. down the group basicity increase. and we know that weak base are good leaving group.
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F is weakest leaving group so almost unreactive
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down the group leaving group ability increase. so F is weakest while I is best leaving group
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got it?
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yes sir now I n clear 🙏🙏
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Dinesh khalmaniya 1

X is any halogen generally Cl, Br
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why not F sir
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Grignard reagents are, in general, alkyl magnesium halides. It can be represented as RMgX; where R: an alkyl chain and X: a halide(maybe chloride, bromide or iodide)
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why we can't use F sir
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Priyanshu kumar

The halide may be Br,Cl and I but not F
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check simun
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why not F
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The C−X bond energy is maximum in CH3F hence, fluoride is less reactive to form the Grignard reagent with Mg.
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got simun??
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no
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where you have problem??
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C-X bond energy is maximun in CH3F bond...and when we go down the group the bond dissociation energy decreases due to increases in bond length
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So down the group halogen group favours
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but F becomes almost unreactive
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yes sir
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😊👍
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