TAP CHi KHOA HOC DHSP TPHCM Pham Van Hoan va tgk SU'''' DUNG KHAI NIEM D 6 N G PHAN TRONG DAY HQC HOA HQC d TRlTOfNG PHO T H 6 N G PHAM VAN HOAN'''', NGUY§N TH! HLfdNG" T 6 M TAT Bdng phdn Id Men tuang hda[.]
TAP CHi KHOA HOC DHSP TPHCM Pham Van Hoan va tgk SU' DUNG KHAI NIEM D N G PHAN TRONG DAY HQC HOA HQC d TRlTOfNG PHO T H N G PHAM VAN HOAN', NGUY§N TH! HLfdNG" T M TAT Bdng phdn Id Men tuang hda hoc thu vi Hda huu co Tuy nhien, thuc li Men cdn cd nhiiu bat cap viec hiiu ro su khde biet giua cdc khdi niem "ddng phin", "ddng phin cau tao", "ddng phin hinh hpe" dgy hoe Hda hoc Huu ea a trudng phd Ihdng Viec sii dung dung dan cdc khdi niem lien quan vi ddng phdn Irong gidng dgy hda hge se giup cho hoc sinh ndm duoc bdn chat cdc vdn di hda hoe vd gop phdn phdt triin lu diQT logic cho hoe sink Bdi viit ndy gdp phdn giiip cho gido vien (vd cd hoc sinh) hiiu sdu sdc han ve mat Men luang hda hoc rdt li thu, gdp phdn dgy (vd hoc) mdn Hda hoc tdt han Tit khoa: ddng phin, cdng thdc ciu t^io, ding phin ciu tao, ding phin hinh hpc ABSTRACT Using isomers concept in teaching organic Chemistry in high schools Isomer is an interesting chemical phenomenon in Organic Chemistry However, in reality, there are many gaps in understanding the difference between the term "isomer" , "structural isomer", "geometric isomers" in Organic Chemistry Teaching in high school The proper use of the related concepts of isomers in chemistry teaching will help students grasp the nature of the chemical problems and contribute lo developing logical thinking for students This article provides teachers (and students) with a deeper understanding of an interesting chemical phenomenon, enhancing the teaching and learning of chemistry Keywords: isomer, structural formula, structural isomers, geometric isomers Trong ndi dung Hda hpc huu ca cua chuong ttinh hda hpc d trudng phi thdng, "ding phin" li mpt ttong nhihig khii niem dupc nghien eiiu diu tien, la mdt ttong nhiJng npi dung co bin ttong thuyet ciu tao hda hpe Khii niem niy cung li mdt ttong nhung khii niSm ca bin dupc sii dimg lam nen tang ttong day hpc Hda hpc hdu co DS su dung khii niem ddng phan mdt cich hieu qua ttong day hpc, giio viSn cin hieu mpt each sau sac npi dung vi y nglua ciia khii niSm, so sinh va phin biet chinh xie eic loai ddng phan ciu tao (ddng phin mach eacbon, ddng phin nhdm chirc, ddng phan vj tri nhdm chirc) vi ddng phin lap thS (ddng phan hinh hpc, ddng phin quang hpc), lam rd mdi quan he giiia ddng phan ciu t ^ va ddng phin lap the, phan biet duac khii niem eau tao hda hpe va ciu tnic hda hpc vi nam vimg dupc nhiing npi dung ciia thuySt ciu tao hda hpc Giai bii tip Hda hpe li mdt ttong nhiing phuang phip dn tip, ciing cd kiin thire • PGS TS, Tru&ng B^i hpc ThQ et Hi NOi; Email: pvhoan@moet.edu.v " Cip nhan, Sd Giio due v i BSo tao Ninh Binh 159 Y kien trao do! sS 7(85) nim 20im vi ren luyen kT ning rat hieu qua; thdng qua viec giii bii tap, hpc sinh (HS) dupe dn tip kiin thire, ren luyen thSm vi ki nang hpc tip vi gdp phin hoin thien nhin cich [1] Bai tip Hda hiiu ca cd rit nhiiu uu diem ttong viec phit trien nang lite tu duy, nhit la phit ttiin cic thao tic tu logic cho HS nhd viec cd nhieu chit cd cdng thiic cau tgo khic img vdi ciing mdt cdng thuc phan tu (cic ddng phin ciu tao) m i hpc sinh ed thi xic nhan dupc thdng qua die diem ve tinh chit Khai niem ve ding phan va bai t?p lien quan din khai nif m 1.1 Khai nifm ve dong phan Trudc diy, khai niem ddng phin dupc djnh nghla "la nhOng chat cd cimg cdng thuc phin tu nhung khic vi edng thiic ciu tao"[3] Djnh nghla ehi diing ttong gidi ban hep, vi nd da bj miu thuin tii lieu [3] xet din cie ddng phin hinh hpc cua anken, ttong dd cic cap ddng phin cis - trans li nhiing chat cd cimg cdng thuc ciu tao Hien nay, khii niem ding phin dupe diSn dat chinh xic hon: "Nhiing chit khae cd cimg edng thiie phin tit dupc gpi la nhiing chit ddng phin" [4] Trong chuang ttinh mdn Hda hpc d trudng phd thdng, nhimg yeu ciu vS chuin kiin thirc kT nang (KT - KN) eua phin Hda hilu co ySu ciu hpc smh cin phin biet ehinh xie cac loai ddng phin mdt cich ro ring Cd loai chit ddng phin: ddng phan ciu tao vi ddng phin ciu hinh (ttong chuang trinh phd thdng, ddng phin cau hinh chi dS cap din ddng phin hinh hpe) Nhu vay, ddi vdi hpc sinh phd thdng, khii niem "ddng phin" se bao gdm ci "ddng phan ciu tao" vi "ddng phin hinh hpe" "Ddng phin ciu tao" gdm ding phin vi mach eacbon (mach hd, mach vdng - ed phin nhanh vi khdng phin nhinh), ddng phin vi loai nhdm chire (ed thS coi USn ket ddi, liSn kit ba ciing thude nhdm ehiic), ddng phin vi vi tri nhdm chitc ttong mach eacbon, ddng phin vS vj tri tuang ddi cua cic nhdm chitc (nSu phan tu cd nhieu nhdm chile) 1.2 Sa luac vi bdi Igp lien quan den khdi niem dong phdn Trong sich giio khoa mdn Hda hpc Idp 11 vi 12, cac bii tap lien quan den khai niem ddng phin cdn it, thudng chi dupc dS xuit vdi ySu ciu d mirc hieu khii niem (phin biet cac chit ddng ding, chit ddng phin, khii niem vS cic chit ddng phin ) Trpng nhiing bii tip djnh lupng, khii niem ddng phin ciing rit it xuit hien De ed thS dat dupc chuin KT - KN neu tren, ngudi GV phii linh boat ttong viec thiit ki cie bai tip, su dung chiing mpt each hpp li ddi phii hap vdi npi dung bii hpc vi ddi tupng HS Day hpc vi cic khii niem hda hpc vi sir dung cac khii niem ttong day hpc la mpt ttong nhihig kT nang day hpc quan ttpng cua ngudi giap vien (GV) Hda hpc KT ning day hpe cd thi dupc hinh thinh thdng qua viee thiit ki eae dang bii tap khae liSn quan din khii niem ding phin di sir dung ttong cic bii hpc De lim dang bii tap niy, hpe sinh ein nim dupe nguyen tic viit cdng thiic cau tao cua cic loai hpp chat hOu eo vi nguyen tic gpi ten Tir cdng thiic phin tir, xic djnh dupc mdi quan h$ giiia 160 TAP CHi KHOA HOC DHSP TPHCM Phgm Vin Hoan vi Igk cac nguySn tu eacbon, hidro vi cie nguyen td khic, xic djnh dupc dp khdng no eua chat, tir dd xic djnh dupc eic Ipjii hpp chit thda man Tuy nhien ttong th\re ti, ci ddi vdinhiSu giio vien ciing ehua hoin toin hiiu mdt cich diy du, chinh xic vi khai niem ddng phan Su- dung bai tip vi ddng phan day hoc Hoa hoc 2.L sa difng khdi niim ddng phan dgy hoc Hda hoc l&p 11, giip HS nim vOng nil dung cac khii niem cua Hda hUu ctf u Giup HS nam vOng ndi dung nhiing lugn diim cua thuyit ciu tgo hog hoc Trong day hpc Chuang - Dai cuang vi Hda hpc him ea vi hpp chit hiiu co (HCHC), HS cin nim viing npi dung ThuySt ciu tao hda hpc: Trong phin tu hap chit hOu CO, cic nguyen tii C cd thi lien kit vdi tao thinh mach eacbon; mach eacbon cd thS khdng cd nhinh, phin nhanh hoje mach vdng; phin biet "ding ding" vdi "ddng phan" ^ Ngoai djng bai tip thudng dung sich giao khoa (Cie chit sau diy nhimg chit nio la ddng ding,_ ddng phin cua ), GV cd thi hudng din HS viit cdng thitc ciu tao cua cie chit ddng phin Thi du - ViSt cdng thuc eau tao eua eac hidrocacbon cd cdng thiic phan tir C4H8 - Cd nhimg cdng thuc ciu tao nio iing vdi edng thiic phan tu CjHjO, C3H6O2? b Phdn biet vd chinh xdc hda cdc khdi niem vi cdc chdt ddng phdn, logi dong phdn pidng thudng, hpe sinh (vi di nhiiu giio viSn) hay bj nhim lin giila cic thuit ngO ve ddng phan Cin phan biet ciu hdi vi "cie chit ddng phan ciu tao" vdi "cac chit ddng phan" Thi du Phan biet ddng phan ciu tao, ding phan hinh hpc qua bii tip vi ddng phin cua cic chit cd cdng thirc phin tu dang C„H2„ Vdi dd khdng no bing 1, cae hidrocacbon niy cd thi thude loai anken (phin tu ed lien kSt ddi C=C) hoac monoxicloankan (phan tu cd vdng no), dd ngoai cie ddng phin ciu tao cdn cd thi cd mdt sd ddng phan hinh hpc Ddi vdi trudng hpp ilng vdi cdng thiic phin tu C4H8 cd cic ding phin ciu tao li: (i) cac anken (3 dong phin: but-l-en, but-2-en va 2-metylpropen); (ii) eic xicloankan (2 ding phin: xiclobutan vi metylxiclopropan) Ngoii ra, but-2-en edn iing vdi cap ddng phin hinh hpe: cK-but-2en va fram-but-2-en Tiiy theo yeu ciu ttong bai ma GV cd thi thiit ki ciu hdi cho cic yeu ciu: Viit cdng tiuie vi ten cua cic anken ddng phan ciu tao cd CTPT la C4Hg (3 anken); Viit cdng thirc ciu tgo/ciu tiTic vi tSn cua cic anken ddng phan cd CTPT li C4Hg (4 anken, ttong dd ki ci ddng phin hinh hpe); 161 y kien trao do! Sd 7(85) nim 201^ Viit edng thiic ciu tao/cau tnic va ten gpi cua eac hidrocacbon cd CTPT li C4Hg (4 anken, ttong dd ki ei ddng phin hinh hpc va xicloankan); t Xdc dinh cdc chirc hda hoc Thi du Viit cdng thirc ciu tao vi gpi ten cic chit cd cimg cdng thilc phin tut C4H10O GV cin hudng dan HS vi viee cin nhan thiy cdng thdc tten cd thinh phin C„H2,H.20 vdi dp khdng no bing zero Viy edng tiuie niy ling vdi cic chit tiiudc loai ancol hoac ete no, dan chiic, mgcb hd Tir dd viit dugc CTCT cua eac chit tuong ilng gom: aneol (4 ddng phin ciu tao) vi ete (3 ddng phin ciu tgo) Thi du Cd bao nhiSu hpp chit dan chite, ddng phin ciia cd cimg cdng tiuie phin tit C3H6O? Vdi ciu hdi cin xic djnh dupc: cic chit tten ed dp khdng no bing 1, dd ed thi li cic hpp chit mach hd thupc loai andehit hoae xeton no dan chirc, hoac ancol khdng no don chuc vi ancol no, don chiic, mach vdng Cic chit dd li: CH3CH2CHO, CH3COCH3, CH2=CHCH20H vi xielo-CaHjOH Trudng hpp ehua xuit hien ding phin hinh hpc Thi du Cd bao nhiSu chit ddng phin ciu tao, phan tii cd mot loai nhdm chiic, cd cung cdng thiic phin tu C4HgO? LTng vdi dp khdng np bing 1, phin tu cae chit cd thi ed liSn kit ddi C=C hoac lien kit ddi C=0 hoae vdng no Va nhu vay cd thi cd ci ding phin hinh hpc xung quanh liSn kit ddi C=C hoae vdng no Phin tu cd nguySn tit O nen cd the ed nhdm andehit hoac xeton hoac ancol dan chuc (vi cd thS tinh ci eac ete don chde nila) Tir ed thi viit dupc cdng thire ciu tao vi ciu hinh cua cac chit nhu sau: Andehit no, don chiic mach hd (2 chit ddng phin ciu tao); xeton no, don chitc, mach hd (1 chit); ancol khdng no, don chuc, mach hd (3 ddng phin ciu tgo) vi ancol no, don chile, mach vdng (4 ddng phin ciu tao) Ngoii ra, ddi vdi HS kha, gidi, GV cd the hudng dln/ySu ciu viit them cdng thuc ciu tao eua cic ete ddng phin, eic ddng phan hinh hpe niia 2.2 Sur dung bii tap ve khdi niem ding phdn giip HS ndm vung ve tinh chat cia cdc chit hUu ca, idm cdc bdi tgp linh todn a Thi du Hdn hpp X gdm mdt sd chit mach hd, ding phin cua nhau, phan tir chiia C, H, O vi chi cd mdt loai nhdm chile, dSu tie dung dupe vdi natri Ti khdi hoi cua X so vdi hidro bing 44 ViSt cdng thiic ciu tao eua eac chit cd the cd ttong X Vdi M = 88 g/mol, tie dung dupc vdi natri chiing td eac chit thupc Ipai axit cacboxylic hoac ancol NSu la axit thi nhdm -COOH cd khii lupng 45 nen ehi li eac axit cacboxylic don chiic R-COOH Vdi gdc R cd MR = 43 irng vdi nhdm C3H7, cic axh dd li : CH3CH2CH2COOH vi (CH3)2CHCOOH - diu la cie axit no, mach hd 162 TAP CHi KHOA HOC DHSP TPHCM Phgm Vin Hoan vi tgk Neu la ancol R(OH)„: vdi n =1, gdc R cd MR = 71 tuang iing vdi gdc hidrocacbon hoa trj 1-C5H1,: gim ding phaii eiu tao (GV hudng din HS viit cae cdng ttiirc ciu tgo); vdi n = 2, MR = 54 ling vdi gdc hda tti II-C4H6- tuong ling vdi aneol ding phin eau tgo mgch hd C4H6(OH)2, ttong dd cd mdt aneol cd ding phin hinh hpc * GV ed tiie tiiiet kS bii tap khic hrong tu vdi dil kien da cho bing cich giu nguyen dti kien "Cie chit ddng phan ciu tgo eua nhau, ehiia C, H, O phan tii va ed M = 88 g/mol", tiiay ddi du kiSn vi tinh chit cua cic chit ttong hdn hpp (thi du: cac chit tic dung dupe vdi dung djch NaOH- dd gdm cic axit cacboxylic don chile vi este dan chuc) b Thi du Viet cdng thilc ciu tgo ciia cic chit ding phin cd edng thirc phin tit CjHiiN tie dung vdi axit HNO2 d - I0°C sinh khdng miu Cic chat cd tmh chit tren thude logi amin bac 1, mgch hd, cd cdng thirc eiu tgo C4H9NH2 Nhu vay ed chit ddng phin eiu tgo thda man GV hudng din HS cd thi viSt cdng thiic ciu tao cua cic amin niy tuong tu nhu vdi cic ancol C4H9OH d thi du tten * GV cd the thay ddi ciu hdi: Cd bao nhieu chit ding phin ciu tgo cd cdng thiic phin til C4H1 ,N cho tiiem dung dich axit HNO2 (hdn hpp axit HCl vi NaN02) d 10 C khong sinh khdng miu Khi dd ciu tti Idi Ii cic amin bic II, bac III 2.3 Md rong kiin thiic thdng qua khdi niem dong phan Khi ndi ve eic chit ddng phin, cin nhd mdt si cap chit ding phan phi biin: anken - monoxicloankan; ankadien - ankin; aneol - ete; andehit - xeton; axit - este; ngoai ra, ttong eac dS thi dai hpc thudng ed md rdng ySu ciu, ed them cic chit ding phan andehit - xeton - aneol khdng no, mach hd - ancol no mgch vdng; ddng ding benzen - ankadiin [4] Trong mdt vii dS thi tuySn sinh dgi hpc, cao ding, vin di ding phin hinh hpc ddi ciing md rdng hem chuong ttinh, thi du [5]: K ^CHs =C Br'^c= H ,C=C^ B^" 'CH3 va Hai ddng phan tten khdng gpi Ii ddng phan cis-trans (dua vdo su phdn bd cua mgch cacabon xung quanh lien kel ddi C=C), mi thude loai ding phin Z-E {dua tren tieu chi ve sd hieu nguyen tir ciia cdc nguyen td lien ket true tiep vdi nguyen tir C cua lien kit ddi) Hien nay, vin cd nhiing su nhim lan giQa "ddng phin cua X" va "nhiing chit ding phan cd eung cdng thitc phin til" Ching hgn, ed thi liy tiii du: ling vdi cdng tiiuc phin tu C4H10 cd ding phin ciu tgo Ii «-C4H|o vi iso-CfUm- Niu ta liy chit X cd cdngtiiuTCphin tii C4H10 di lim thi nghiSm thi chit X niy da la «-C4H,i, hoae la isoC4H,o Khi do, si dong phan cua X se Ii chit cdn lgi (1 ding phan) Cbinh vi nhiing su nhim lin giila "ding phin ciia X" va "nhang chit ddng phan 163 Y kien trao do! So 7(85) nim 201^ cd cimg cdng thirc phin tii" nSn di ed nhihig sai sdt ttong cic sich tham khio, day hpc sinh, vi thim chi ttong cic de thi Thi du, ttong dS thi hjySn sinh dgi hpc khdi A, nim 2009- mdn Hda hoc, mS dS 175, cd ciu si 18 nhu sau: Cho 10 gam amin don chiic X phin img hoin toin vdi HCl (du), thu dupc 15 gam mudi Sd ddng phin ciu tgo ciia X li A B.8 C.5 D.7 Lai ban- CTPT cua X li C4H|,N iTng ydi CTPT niy cd amin ddng phan cau tgo, ttong dd cd ca X Nhu viy, ding phan ciu tao cua X ehi la (Dip in D), nhtmg dip in ciia di thi lgi li (Dip in B) Mdt su nhim lln tuong tu thi hien ttong di tiii tuyin sinh dgi hpe khdi A, nim 2011 - mdn Hda hpc, m i di 318, Ciu 11: "Cho 13,8 gam chit hHu co X cd cdng thitc phan til C7H8 tic dimg vdi lupng du dung djch AgNOj ttong NH3 thu dupe 45,9 gam kit tua X cd bao nhieu ding phin ciu tgo thda man tinh chit ttSn ? A B.6 C.4 D.2." Dap in ciia di thi li C Ldi bdn: Dip an cua di thi khdng dung Vi cdng thiic eau tao thu gpn cua X li HCsC-CjHe-CsCH LTng vdi CTCT thu gpn cd ding phin ciu tgo ingch hd vi ddng phin ciu tao mgch vdng, ttong dd ed X Nhu viy, till X thi cdn ding phin ciu tao ciia X, dd phii li dip in A Cd le tic gii di thi ehi tinh ding phan ciu tgo mgch hd, vi tinh ea X dd Cung gap ldi nhu ttSn ttong dS thi tuyen sinh dgi hpc khdi A, nim 2012 - mdn Hda hpe, ma di 296, Ciu 35: "Hidro hda hoin toan hidrocacbon mgch hd X thu dupc isopentan Sd edng thuc ciu tgo cd the ed eua X la A B.7 C.4 D.5." Ldi bdn: Ciu sai vi vdi mdt chit X cu thi thi ehi cd edng tiuie ciu tgo tucmg ling, dd khdng tbi ed khii niem "Sd cdng thuc ciu tgo cd the cd ciia X" Cd thi sua ciu ttSn "Hidro hda hoan toin mdt hdn hpp X gdm cac hidrocacbon mgch hd tiiu dupc chit nhit li isopentan Sd hidrocacbon tdi da ttong hdn hpp X li A B.7 C.4 D.5." Mdt vii thi du nira eho thiy edn cd sir nhim lin vi ciu tao vi cdng tiuie eiu tao Trong di thi tuyin sinh dgi hpc khdi A, nim 2014 - mdn Hda hpe, ma di 259, Ciu 16: "Ancol X no, mgch hd cd khdng qui nguySn tu eacbon ttong phin tu Biit X khdng tic dyng vdi Cu(0H)2 d dieu kien thudng Sd edngtiiitcciu tao ben phii hpp vdi X li A B.2 C.3 D.5." Vdi dap an diing la D 164 TAP CHi KHOA HOC DHSP TPHCM Phgm Vin Hoan vi Igk Ldi bdn: Ciu niy sai nhiiu chi Thil nhit, vdi mpt chit X eu thi thi chi cd cdng thiic ciu tgo tuong irng, dd ciu hdi la vd nghTa; thii hai, khdng cd "cdng thiic cau tjo ben" mi chi cd cau t?o bin; cdng thuc ciu tgo la edng thirc biiu diln ciu tgo cua chit NSu siia eau tten "Hdn hop X gim cae ancol no, mgch hd, ed khdng qui nguySn til caebon ttong phin tit Biit X khong tie dimg vdi Cu(0H)2 d diiu kien fliudng Sd ancol tii da cd ttong X Ii A B.2 C.3 D.5." Khi do, X gim cac ancol: CH3OH, C2H5OH, C3H7OH (2 ddng phan), HOCH2CH2CH2OH nhu dip in D Cd tiie chi rit nhieu ldi nhu vgy ttong cic sach tham khio, vi vd hinh trung di Ii tii lieu tham khao sai cho rit nhiiu giio viSn va hpc sinh Kit lu$n Nhu viy, ed the thiy vi$c xac djnh diing ySu ciu nhan thiic dgy hpe vi cic chit ddng phin li rit thii vj, da dang vi khdng hi don giin Viee xac djnh dung yeu ciu ciia cau hdi, bii tip vi ding phin ddi hdi ngudi GV phii cd nin ting kiin thirc vimg vang, ed ki ning thiet ki vi sii dung cic dgng bai tip cua Hda hpc hilu co ttong day hpc mdi khai thic dupc cic kiSn thuc hda hpc mpt cieh hieu qui, giiip ngudi hpc van dung linh hogt kiin thiic cua minh hpc tgp va giiip cho viee thi tit nghiep, thi tuyin sinh vio cao ding, dgi hpc dat hieu qui cap DS giiip khic siu kiin thire Hda hpc cho hpc sinh, rit cin sii dung tinh chit cua chit de ndi v6 cac chit ddng phan TAI U%V THAM KHAO Nguyen Cuong, Nguyen Manh Dung (2002), Phuang phdp dgy hoc Hda hoc Nxb Dgi hpc Su phgm Ha Ndi Nguyen Hdu DTnh (ehu biSn) (2008), Dgy vd hoc Hda hoc 11 theo hudng ddi mdi, Nxb Giio dye Hi Npi Trin Qudc San, Le Xuan Trpng (2000), Hda hoc 11, Nxb Giio dye Nguyen Xuan Trudng vi tgk (2008), Hda hoc 11, Nxb Giio due Bp Giio due vi Dao tgo Be thi tuyen sinh dgi hge eao ddng khdi A, mdn Hda hoc cdc nam 2010-2014 (Ngiy Ida so?n nh$n duvc bii: 31-8-2015; ngiy phin bi$n dinh gii: 27-10-2015: ngiy chip nh$n ding: 22-9-2016) 165 ... diim cua thuyit ciu tgo hog hoc Trong day hpc Chuang - Dai cuang vi Hda hpc him ea vi hpp chit hiiu co (HCHC), HS cin nim viing npi dung ThuySt ciu tao hda hpc: Trong phin tu hap chit hOu CO,... chitc (nSu phan tu cd nhieu nhdm chile) 1.2 Sa luac vi bdi Igp lien quan den khdi niem dong phdn Trong sich giio khoa mdn Hda hpc Idp 11 vi 12, cac bii tap lien quan den khai niem ddng phin cdn... chinh xic hon: "Nhiing chit khae cd cimg edng thiie phin tit dupc gpi la nhiing chit ddng phin" [4] Trong chuang ttinh mdn Hda hpc d trudng phd thdng, nhimg yeu ciu vS chuin kiin thirc kT nang (KT